Abnormality determining method, abnormality determining apparatus, and image forming apparatus

ABSTRACT

An image forming apparatus is capable of specifying the type of an occurring abnormality to a certain extent while avoiding the increasingly complicated control that is cause when a plurality of abnormalities is detected individually according to the presence of their respective causes. A normal group data set, which is a collection of normal value combination relating to grouped information constituted by a plurality of information of differing types, is stored in RAM or ROM serving as information storage device of a control unit. At least two or more sets of grouped information, including first grouped information constituted by a plurality of different types of information, and second grouped information constituted by a plurality of information in a different combination to that of the first grouped information, are obtained from the RAM, the ROM, various sensors, and an operation display unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an abnormality determining apparatusfor determining the presence of an abnormality in a detection subject onthe basis of stored information stored in information storage means, anda result obtained by information obtaining means for obtaininginformation about an object, and also to an abnormality determiningmethod and an image forming apparatus.

2. Description of the Background Art

In an image forming apparatus such as a copier, facsimile device, orprinter, maintenance is required to replace consumables (toner, forexample) and components (a photosensitive body, for example), repairfaults, and so on. When a fault occurs, all or a part of the functionsof the device must be halted from the occurrence of the fault to thecompletion of repairs, causing a great time loss for the user. It istherefore desirable to predict the occurrence of a fault in the imageforming apparatus, the end of the life of a component, and so on inorder to provide the user with a maintenance preparation period, therebyreducing the amount of downtime. Examples of an image forming apparatuswhich is capable of making such predictions include the device disclosedin Japanese Unexamined Patent Application Publication H5-281809 (PriorArt 1), for example.

In the image forming apparatus disclosed in this Prior Art 1, drivingload information regarding a driving source is detected, and earlydetection of an abnormality in the driving system is performed bycomparing the detection result with a standard value. According to thisconstitution, by detecting an abnormality in the driving system before afault occurs, a user can be provided with a preparation period toprepare for maintenance to the driving system.

A Mahalanobis Taguchi System, described in the Japanese StandardsAssociation publication “Technical Developments in the MT System” byGenichi TAGUCHI (Prior Art 2), is known as a method of measuring thedegree of normality in the state of an object. This MTS method measuresthe degree of normality in the state of an object in the followingmanner. First, a plurality of combined normal values relating to a groupof information comprising a plurality of types of information indicatingthe state of a detection subject is obtained, and a normal group dataset is constructed therefrom. To take a medical examination as anexample, first combined normal values comprising the gender, variousblood test results, height, weight, and so on of a healthy person areobtained in advance from a plurality of healthy people, and a normalgroup data set is constructed therefrom. Next, a multidimensional spaceis constructed on the basis of the normal group data set. TheMahalanobis distance, which indicates the position of the groupedinformation obtained from the detection subject in this multidimensionalspace, is then determined, and an evaluation is performed to determinethe degree of similarity between the grouped information for thedetection subject and the normal group data set. According to this MTSmethod, the degree of normality of the detection subject can bedetermined comprehensively on the basis of the correlation among thevarious information.

The image forming apparatus disclosed in the aforementioned Prior Art 1detects in particular driving system abnormalities caused by anexcessive load being placed on the driving source. Abnormalities in thedriving system may have numerous other causes. Any abnormality can bedetected by monitoring the presence of its cause. However, if thepresence of the cause of each abnormality is monitored and detectedindividually, the control required for this monitoring becomes extremelycomplicated, and as the number of types of abnormality to be detectedincreases, the control becomes ever more complicated.

Hence the present inventors are currently developing a novel imageforming apparatus which is used to determine an abnormality bydetermining the Mahalanobis distance according to the aforementioned MTSmethod, on the basis of a normal group data set stored in informationstorage means and the results obtained by sensors and the like of aplurality of types of information. According to this image formingapparatus, the degree of normality is evaluated on the basis of aMahalanobis distance determined from a plurality of types of informationrelating to various abnormalities, rather than detecting a plurality ofabnormalities individually according to the presence of their respectivecauses, and hence the occurrence of these abnormalities can be detectedcomprehensively. In so doing, the complicated control required to detecta plurality of abnormalities individually according to the presence oftheir respective causes can be avoided.

However, since this image forming apparatus detects the occurrence ofvarious abnormalities comprehensively by perceiving the degree to whichthe apparatus has deviated from a normal state, it is difficult tospecify the type of the abnormality. As a result, the maintenanceresponse following the detection of the abnormality becomes complicated.

Further, a remote fault diagnosing system is installed in the imageforming apparatus disclosed in the aforementioned Prior Art 1. In thisremote fault diagnosing system, basic diagnosis data transmitted from aplurality of image forming apparatuses serving as diagnosis subjects arereceived in a central diagnosing apparatus, and various abnormalities inthe individual image forming apparatuses are diagnosed on the basis ofthese basic data. These various abnormalities include a paper feedingabnormality, an image quality abnormality, and so on. By diagnosing thevarious abnormalities respectively, a fault in the paper feeding systemor image forming system caused by the progression of the diagnosedabnormality can be predicted before its occurrence. Moreover, whendiagnosing the various abnormalities, the remote fault diagnosing systemtakes into account the proficiency of the user of the image formingapparatus and the degree of perception of the fault. This is due to thefollowing reason.

For example, a user who is highly conversant with the image formingapparatus may be able to repair a fault in the image forming apparatusthat a general user could not repair. In such a case, the user would notcontact a repair service organization to request repairs. If aserviceperson is dispatched nevertheless due to the prediction of theoccurrence of the fault, the resulting wasted labor would lead to anincrease in service costs. Moreover, depending on the type of fault,each user has a widely differing perception thereof. For example,one-user may suspect a fault in the paper feeding system even when apaper jam occurs rarely, whereas another user may not suspect a fault inthe paper feeding system even when paper jams occur comparativelyfrequently. In the case of the latter user, repair requests are rarelymade, even if a serviceperson is dispatched at the stage when theabnormality in the paper feeding system has barely begun to occur. Thismanner of dispatch also leads to an increase in service costs. Hence bytaking into account the proficiency and degree of fault perception ofthe user, abnormality diagnosis which is suited to each individual useris performed, leading to a reduction in service costs. Note that as aresult of dedicated research, the present inventors have discoveredthat, from among various abnormalities, the degree of perception of eachuser varies particularly widely in regard to an abnormality in the imagequality.

This remote fault diagnosing system diagnoses each of a plurality ofabnormalities occurring in the diagnosis subject image forming apparatusindividually. Hence as the number of types of abnormality to bediagnosed increases, the calculation amount required for the diagnosisincreases, making control more complicated. Moreover, providing the userwith a preparation period required to prepare for maintenance in orderto reduce downtime is desirable not only in an image forming apparatus,but in various other apparatuses such as manufacturing devices andelectric appliances.

Hence the present inventors are currently developing a novel abnormalitydetermining apparatus in which various abnormalities in a detectionsubject such as an image forming apparatus are determinedcomprehensively as a single general abnormality, rather thanindividually. The presence of the general abnormality is determined onthe basis of the aforementioned Mahalanobis distance, for example.According to the abnormality determining apparatus constituted in thismanner, when at least one of the various abnormalities occurs, thegeneral abnormality is determined comprehensively as “abnormalitypresent”, and thus increasingly complicated control due to an increasein the number of types of abnormality in the determination-subject canbe suppressed.

However, when the general abnormality is determined as “present” using amethod of perceiving the degree of deviation from a normal state, aswith the Mahalanobis distance, rather than perceiving the presence ofindividual abnormalities, it is difficult to specify the type ofabnormality that has occurred from among all of the abnormalities thatmay be incorporated into the general abnormality. As a result, themaintenance response following a determination of “general abnormalitypresent” becomes complicated.

Furthermore, the abnormality determining apparatus is unable todetermine various abnormalities in consideration of the user'sproficiency and degree of fault perception. As a result, even when anattempt is made to specify the type of the abnormality that hasoccurred, the abnormality determination precision is not always suitedto the user, and depending on the user, abnormalities may be detectedunnecessarily, the detection timing may be too late, and so on.

In an image forming apparatus disclosed in Japanese Unexamined PatentApplication Publication H05-100517 (Prior Art 3), the life of aphotosensitive body is predicted by monitoring the potential state ofthe photosensitive body. More specifically, forecasts are made regardingfaults in and the lifetime of limited locations within the system thatmonitors this information. This is an important process in itself, butwith this method, although it is possible to determine abnormalities inthe monitored locations, it is not possible to predict device problemshaving multiple causes. Particularly in this case of anelectrophotographic image forming apparatus, balance is maintained overthe entire apparatus by means of control in which process parameters aremoved as a whole through process control, and hence it is impossible todetermine abnormalities simply by monitoring a single piece ofinformation.

Further, in an image forming apparatus disclosed in Japanese UnexaminedPatent Application Publication H08-137344 (Prior Art 4), the state ofthe image forming apparatus is determined by detecting a check patternon a photosensitive body to determine whether or not the image thereofis normal. With this method, abnormalities on the upstream side of theimage forming operation, including the photosensitive body, can bedetermined in composite, but abnormalities on the downstream side cannotbe determined at all.

Meanwhile, it is also possible to obtain a plurality of types ofinformation expressing the state of an image forming apparatus,calculate a single index value from the plurality of types ofinformation, and determine a change of state in the image formingapparatus on the basis of temporal variation data of the index value.With this method, if information is obtained in advance for eachlocation of the apparatus as the plurality of types of information, theoverall operational state of the apparatus can be monitored at alltimes. Further, when the plurality of types of information varies as awhole, the apparatus can be determined as normal if the informationvaries as a whole while maintaining a normal balance, and determined asabnormal if not. The important point of this state determining method isthat “a calculation parameter for calculating an index value isdetermined using only a plurality of types of data gathered when theimage forming apparatus is in a normal state”. The calculation parameteris a reference expressing a normal state, whereas the index value, whichis calculated after the calculation parameter is fixed using temporalmomentary data (or the average data of a fixed time period), has acharacteristic whereby it becomes larger as the image forming apparatusmoves further from a normal state. Thus the location of the imageforming apparatus which is moving toward an abnormality can bedetermined.

A problem which arises at this time is “when should the calculationparameter be fixed?”. In such a determination, it is presumed that anormal data set obtained in a factory environment prior to shipping, forexample, would be insufficient. This is because an actual usageenvironment on the market is considered to differ from a factoryenvironment, and hence, by obtaining a large number of normal data setsin the actual usage environment, the calculation parameter can bedetermined appropriately for the actual usage conditions in the customerlocation. At this time, a device or system is required to determinewhether or not the image forming apparatus is in a normal state. Thecalculation parameter is defined originally to determine the state of adevice, but the normal state of the device must be ensured using othermeans until the calculation parameter is fixed.

SUMMARY OF THE INVENTION

The present invention has been designed in consideration of thebackground described above, and it is a first object thereof to providean abnormality determining method which is capable of specifying thetype of an occurring abnormality to a certain extent while avoiding theincreasingly complicated control that is caused when a plurality ofabnormalities is detected individually according to the presence of therespective causes thereof, as well as an abnormality determiningapparatus, and an image forming apparatus.

A second object of the present invention is to provide an abnormalitydetermining method and abnormality determining apparatus which arecapable of determining the presence of an abnormality with a precisionsuited to each individual user, while suppressing increasinglycomplicated control occurring when various abnormalities are determinedindividually and an increasingly complicated maintenance responsefollowing a determination.

A third object of the present invention is to provide an abnormalitydetermining method and abnormality determining apparatus which arecapable of determining a calculation parameter at an arbitrary timingafter a plurality of types of information has been obtained continuouslyover time on the market, and thereby determine an element which isapproaching an abnormal state.

An abnormality determining method of the present invention comprises aninformation storing step for storing information about an object in aninformation storage device; an information obtaining step for obtaininginformation about an object using information obtaining device; and adetermining step for determining the presence of an abnormality in adetection subject on the basis of the stored information in theinformation storage means and the obtained information obtained by theinformation obtaining device. In the information storing step, a normalgroup data set, which is a collection of normal value combinations ofgrouped information constituted by a plurality of different types ofinformation, is stored in the information storage device. In theinformation obtaining step, at least two or more sets of groupedinformation, comprising first grouped information constituted by aplurality of different types of information and second groupedinformation having a different combination to that of the first groupedinformation, are obtained by the information obtaining device. In thedetermining step, a Mahalanobis distance is determined for each set ofgrouped information on the basis of the normal group data set and theobtained results of each set of grouped information, and used todetermine the presence of an abnormality in the detection subject.

An abnormality determining apparatus of the present invention comprisesan information storage device for storing information about an object;an information obtaining device for obtaining information about anobject; and a determining device for determining the presence of anabnormality in a detection subject on the basis of the storedinformation stored in the information storage device and the obtainedresults obtained by the information obtaining device. A normal groupdata set, which is a collection of normal value combinations of groupedinformation constituted by a plurality of different types ofinformation, is stored in the information storage device. At least twoor more sets of grouped information, comprising first groupedinformation constituted by a plurality of different types of informationand second grouped information constituted by a plurality of informationin a different combination to that of the first grouped information, areobtained by the information obtaining device. The determining devicedetermines a Mahalanobis distance for each set of grouped information onthe basis of the normal group data set and the obtained results of eachset of grouped information, and uses the Mahalanobis distance todetermine the presence of an abnormality in the detection subject.

An image forming apparatus of the present invention comprises an imageforming device for forming an image on a recording medium; and anabnormality determining apparatus for determining the presence of anabnormality in said image forming apparatus. The abnormality determiningapparatus comprises an information storage device for storinginformation about an object; an information obtaining device forobtaining information about an object; and a determining device fordetermining the presence of an abnormality in a detection subject on thebasis of the stored information stored in the information storage deviceand the obtained results obtained by the information obtaining device. Anormal group data set serving as a collection of normal valuecombinations of grouped information constituted by a plurality ofdifferent types of information is stored in the information storagemeans. At least two or more sets of grouped information, comprisingfirst grouped information constituted by a plurality of different typesof information and second grouped information constituted by a pluralityof information in a different combination to that of the first groupedinformation, are obtained by the information obtaining device. Thedetermining device determines a Mahalanobis distance for each set ofgrouped information on the basis of the normal group data set and theobtained results of each set of grouped information, and uses theMahalanobis distance to determine the presence of an abnormality in thedetection subject.

An abnormality determining method of the present invention comprises aninformation obtaining step for obtaining information about an objectusing an information obtaining device; a determining step fordetermining the presence of an abnormality in a detection subject on thebasis of the obtained information obtained by the information obtainingdevice; a calculating step for performing a predetermined calculation onthe basis of the obtained information obtained by the informationobtaining device in the determining step; and a comparing step forcomparing the calculation result of the calculating step to apredetermined threshold, an abnormality being determined to be presentwhen, in the comparing step, the calculation result has reached thethreshold, exceeds said threshold, or falls below the threshold. Thedetermining step includes a general abnormality determining step fordetermining the presence of a general abnormality, which is capable ofincorporating a plurality of types of abnormality, by comparing one ofthe calculation results obtained on the basis of a plurality of types ofthe obtained information to the threshold, and an individual abnormalitydetermining step for determining, only when the general abnormality isdetermined as present in the general abnormality determining step, thepresence of one of a plurality of types of abnormality that can beincorporated into the general abnormality by comparing one of thecalculation results obtained on the basis of at least one of theplurality of types of obtained information to the threshold. Initialsetting is performed on at least one of a plurality of the thresholds,used individually in each of the individual abnormality determiningsteps, in accordance with information regarding a user of the detectionsubject.

An abnormality determining apparatus of the present invention comprisesan information obtaining device for obtaining information about anobject; and a determining device for implementing a predeterminedcalculation on the basis of the information obtained by the informationobtaining device, and determining the presence of an abnormality in adetection subject as present when the result of the calculation hasreached a predetermined threshold, exceeds said threshold, or fallsbelow the threshold. The determining device is constituted to determinethe presence of a general abnormality, which is capable of incorporatinga plurality of types of abnormality, by comparing one of the calculationresults obtained on the basis of a plurality of types of the obtainedinformation to the threshold, and implement processing to determineindividually the presence of one of a plurality of types of abnormalitythat can be incorporated into the general abnormality for each type ofabnormality, only when the general abnormality is determined as present,by comparing one of the calculation results obtained on the basis of atleast one of said plurality of types of obtained information to thethreshold.

An abnormality determining apparatus of the present inve tion comprisesan information obtaining device for obtaining information about anobject; and a determining deviced for implementing a predeterminedcalculation on the basis of the information obtained by the informationobtaining device, and determining an abnormality in a detection subjectas present when the result of the calculation has reached apredetermined threshold, exceeds the threshold, or falls below thethreshold. The determining device is constituted to determine thepresence of a general abnormality, which is capable of incorporating aplurality of types of abnormality, by comparing one of the calculationresults obtained on the basis of a plurality of types of the obtainedinformation to the threshold, and implement processing to determineindividually the presence of one of a plurality of types of abnormalitythat can be incorporated into the general abnormality for each type ofabnormality, only when the general abnormality is determined as present,by comparing one of the calculation results obtained on the basis of atleast one of the plurality of types of obtained information to thethreshold.

A state determining apparatus of the present invention comprises aninformation obtaining device for obtaining a plurality of types ofinformation relating to an operation of a subject device; an index valuecalculating device for calculating a single index value from theobtained plurality of information; and a determining device fordetermining a state of the subject device using the calculated indexvalue. A calculation parameter for calculating the index value isdetermined on the basis of said plurality of types of informationobtained during a normal operation of the subject device. Theinformation obtaining device gathers the plurality of types ofinformation, from which the calculation parameter is derived,continuously during a normal operation when the subject device has beenshipped onto the market.

An image forming apparatus for forming a visible image on a recordingmedium on the basis of inputted image information in accordance with thepresent invention comprises an information obtaining device forobtaining a plurality of types of information relating to an operationof the image forming apparatus; an index value calculating device forcalculating a single index value from the obtained plurality ofinformation; a determining device for determining a state of the imageforming apparatus using the calculated index value; and a statedetermining apparatus for gathering the plurality of types ofinformation continuously during a normal operation when the imageforming apparatus has been shipped onto the market, and determining acalculation parameter for calculating the index value on the basis ofthe plurality of types of information obtained during a normal operationof the image forming apparatus.

An image quality detecting apparatus of the present invention isprovided detachably on an image forming apparatus, for detecting animage quality of an image on a sheet of paper formed with said image,which is discharged from the image forming apparatus and introduced intothe image quality detecting apparatus. The image quality detectingapparatus comprises a paper discharge tray on which paper dischargedfrom the image forming apparatus is stacked; a collection unit forcollecting paper on which image quality detection is complete; aswitching device for switching a paper conveyance direction between thepaper discharge tray and the collection unit; and an image qualitydetecting device for detecting the image quality of an image formed on asheet of paper conveyed to the collection unit side.

A state determining apparatus of the present invention comprises aninformation obtaining device for obtaining a plurality of types ofinformation relating to an operation of an image forming apparatusserving as a subject device; an index value calculating device forcalculating a single index value from the obtained plurality ofinformation; and a determining device for determining a state of theimage forming apparatus using the calculated index value. A calculationparameter for calculating the index value is determined on the basis ofthe the plurality of types of information obtained during a normaloperation of the image forming apparatus, and an image quality detectingdevice for detecting an image quality of an output image to determinewhether or not the image forming apparatus is operating normally on themarket are provided separately to and detachably from a main body of theimage forming apparatus. The image quality detecting device is removedfrom the image forming apparatus after a preset time period has elapsed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription taken with the accompanying drawings, in which:

FIG. 1 is a view showing an outline of the constitution of anelectrophotographic copier serving as an example of an image formingapparatus according to a first embodiment of the present invention;

FIG. 2 is a view showing an outline of the constitution of a printerunit in the copier;

FIG. 3 is a partially enlarged view showing the constitution of a tandemunit in the copier;

FIG. 4 is a block diagram showing a part of the constitution of anelectric circuit in the copier;

FIG. 5 is a perspective view showing the constitution of a thin-filmtype resistance variation element in a temperature sensor of the copier;

FIG. 6 is a perspective view showing the constitution of a resistancevariation element constituted differently to that shown in FIG. 5;

FIG. 7 is a perspective view showing the constitution of a humiditysensor installed in the copier;

FIG. 8 is a sectional view showing the constitution of a vibrationsensor installed in the copier;

FIG. 9 is a view showing an outline of the constitution of aconcentration detecting unit of a toner concentration sensor installedin the copier;

FIG. 10 is a view showing an outline of the constitution of a potentialmeasuring system installed in the copier;

FIG. 11 is a view showing an outline of the constitution of thepotential measuring system for detecting a charging potential that isused in the first embodiment;

FIG. 12 is a flowchart showing a series of processes from a normal dataobtaining process to a matrix transformation process;

FIG. 13 is a flowchart showing a procedure for calculating a Mahalanobisdistance D on the basis of an inverse matrix A and various obtaineddata;

FIG. 14 is a view illustrating communication between the copier and amonitoring sensor disposed in a remote location;

FIG. 15 is a view illustrating communication between an abnormalitydetermining apparatus according to a modification of the firstembodiment, and a copier serving as a detection subject thereof;

FIG. 16 is a view illustrating another modification of the communicationperformed between the abnormality determining apparatus and a pluralityof copiers;

FIG. 17 is an obtained data table illustrating a normal data obtainingprocess;

FIG. 18 is a normalized data table constructed on the basis of theobtained data table;

FIG. 19 is a table showing an example of a relationship betweencategories of abnormality types in the copier of this embodiment, andthe grouped information required to determine the presence of theabnormalities within these categories;

FIG. 20 is a table showing an example of a relationship between eachcategory and a Mahalanobis distance;

FIG. 21 is a block diagram showing the constitution of the main parts ofan electric circuit in an abnormality determining apparatus according toa second embodiment of the present invention;

FIG. 22 is a connection diagram showing an example in which theabnormality determining apparatus is constituted separately to thecopier;

FIG. 23 is a connection diagram showing another example in which theabnormality determining apparatus is constituted separately to thecopier;

FIG. 24 is a view showing an example in which the abnormalitydetermining apparatus is constituted integrally with the copier;

FIG. 25 is a table showing an example of a standard threshold for threethresholds relating to a paper jam, deterioration of a photosensitivebody, and variation in image density in the second embodiment;

FIG. 26 is a table showing an example of a relationship between a userproficiency level and a threshold coefficient;

FIG. 27 is a table showing an example of a relationship between a faultperception level, serving as user information, and the thresholdcoefficient;

FIG. 28 is a table showing a relationship between the user type, thedepartment, and the threshold coefficient;

FIG. 29 is a table showing a relationship between an output image type,an output frequency, and the threshold coefficient;

FIG. 30 is a graph showing an example of a relationship between theMahalanobis distance D of a general abnormality in the copier of thesecond embodiment, and the elapsed time (running time)

FIG. 31 is a graph showing a relationship between the Mahalanobisdistance D and the elapsed time when the general abnormality isdetermined at a time interval of 4 t in the copier exhibiting thecharacteristics shown in FIG. 30;

FIG. 32 is a graph showing an example of a relationship between theMahalanobis distance D and the elapsed time when the frequency ofgeneral abnormality determination is raised at the stage where theMahalanobis distance D for the general abnormality approaches theabnormality detection threshold to a certain extent;

FIG. 33 is a pattern diagram showing an example of a display screendisplayed on an operation display unit of the copier when functionrestriction has been performed by function restricting means;

FIG. 34 is a block diagram showing the constitution of the main parts ofan electric circuit in the abnormality determining apparatus accordingto the second embodiment;

FIG. 35 is a view in which an extended line for facilitatingunderstanding of variation in the Mahalanobis distance D has been addedto a graph showing an example of the relationship between theMahalanobis distance D of the general abnormality in the copier, and theelapsed time;

FIG. 36 is a pattern diagram showing an example of an image output to adata display unit when an abnormality relating to deterioration of aphotosensitive body is detected;

FIG. 37 is a block diagram showing the basic constitution of anabnormality predicting system comprising a state determining apparatuswhich is capable of implementing an abnormality predicting methodaccording to a third embodiment of the present invention;

FIG. 38 is a flowchart showing a basic operation of the abnormalitypredicting system;

FIG. 39 is a flowchart showing a basic operation of an abnormalitypredicting system according to a modification of the third embodiment;

FIG. 40 is a table showing a part of multiple types of data gatheredfrom a copier of the third embodiment;

FIG. 41 is a graph showing movement (temporal variation) of an indexvalue D calculated in the third embodiment;

FIG. 42 is a flowchart for deriving a calculation parameter;

FIG. 43 is a flowchart for calculating an index value and determining astate;

FIG. 44 is an enlarged photograph showing an initial image PT1 of ahalftone dot image formed on recording paper by the image formingapparatus of FIGS. 1 and 2, comprising a 600 dpi writing system;

FIG. 45 is an enlarged photograph of a halftone dot image showing animage PT2 following printing over an extremely long time period undercertain conditions;

FIG. 46 is a graph showing a relationship between the spatial frequencyof human sight and sensitivity;

FIG. 47 is a view showing an outline of the constitution of an imagequality detecting apparatus for measuring fine unevenness in the densityof an image;

FIG. 48 is a characteristic diagram showing a relationship betweendistance in a scanning direction (beam diameter) and a light amount;

FIG. 49 is a graph showing a state of output when an amount of light isoutput with time as a parameter;

FIG. 50 is a graph showing a transformation result (spatial frequencycharacteristic) produced by fast Fourier transformation;

FIG. 51 is a graph showing a visual noise amount;

FIG. 52 is a graph showing a calculated total visual noise amount;

FIG. 53 is a view showing disposal positions of an image quality sensor(image quality detecting means);

FIG. 54 is a flowchart showing the flow of data processing by the imagequality sensor; and

FIG. 55 is a view showing a specific constitutional example of anadditional unit when the image quality detecting means are constitutedseparately as an additional unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail below.Note that in each embodiment, examples in which an electrophotographiccopier (to be referred to simply as “copier” hereafter) serves as animage forming apparatus will be described.

First Embodiment

The first embodiment mainly serves to achieve the aforementioned firstobject of the present invention.

First, before describing an abnormality determining apparatus to whichthe first embodiment is applied, an example of an image formingapparatus serving as the detection subject of the abnormalitydetermining apparatus will be described.

FIG. 1 is a schematic constitutional diagram showing the copier servingas an image forming apparatus which may be used as the detection subjectof the abnormality determining apparatus to which the present inventionis applied. The copier comprises image forming means constituted by aprinter unit 100 and a paper feed unit 200, a scanner unit 300, and anoriginal conveyance unit 400. The scanner unit 300 is attached to thetop of the printer unit 100, and the original conveyance unit 400,constituted by an automatic document feeding device (ADF), is attachedto the top of the scanner unit 300.

The scanner unit 300 reads image information of an original placed on acontact glass 32 using a reading sensor 36, and transmits the read imageinformation to a control unit not shown in the drawing. The control unitcontrols a laser, LED, or the like, not shown in the drawing, disposedwithin an exposure device 21 of the printer unit 100 on the basis of theimage information received from the scanner unit 300 to irradiate fourdrum-shaped photosensitive bodies 40K, Y, M, C with laser recordinglight L. By means of this irradiation, an electrostatic latent image isformed on the surface of the photosensitive bodies 40K, Y, M, C. Thislatent image is then subjected to a predetermined developing process tobe developed into a toner image. Note that the suffixes K, Y, M, Cfollowing the reference numerals indicate black, yellow, magenta, andcyan specifications.

In addition to the exposure device 21, the printer unit 100 comprisesprimary transfer rollers 62K, Y, M, C, a secondary transfer device 22, afixing device 25, a paper discharge device, a toner supply device notshown in the drawing, and so on.

The paper feed unit 200 comprises an automatic paper feed portiondisposed beneath the printer unit 100 and a manual paper feed portiondisposed on the side face of the printer unit 100. The automatic paperfeed portion comprises two paper cassettes 44 disposed one on top of theother inside a paper bank 43, feed rollers 42 for feeding transfer paperserving as a recording medium from the paper cassettes, a separationroller 45 for separating the fed transfer paper and conveying it to afeed path 46, and so on. Conveyance rollers 47 for conveying thetransfer paper to a feed path 48 in the printer unit 100, and soon, arealso provided. The manual paper feed portion comprises a manual paperfeed tray 51, a separation roller 52 for separating the transfer paperon the manual paper feed tray 51 into single sheets and feeding thepaper toward a manual feed path 53, and so on.

A pair of registration rollers 49 is disposed near the end of the feedpath 48 of the printer unit 100. The registration roller pair 49 receivethe transfer paper fed from the paper cassettes 44 or manual paper feedtray 51, and then, at a predetermined timing, feed the paper to asecondary transfer nip formed between an intermediate transfer belt 10serving as an intermediate transfer body and a secondary transfer device22.

When an operator wishes to make a copy of a color image on this copier,s/he sets the original on an original table 30 of the originalconveyance unit 400. Alternatively, the operator opens the originalconveyance unit 400 and sets the original on the contact glass 32 of thescanner unit 300, and then closes the original conveyance unit 400 sothat the original is held down. The operator then presses a start switchnot shown in the drawing. When the original is set on the originalconveyance unit 400, the scanner unit 300 begins to operate after theoriginal is conveyed to the contact glass 32, and when the original isset on the contact glass 32, the scanner unit 300 begins to operateimmediately. A first traveling body 33 and a second traveling body 34then move such that light emitted from a light source in the firsttraveling body 33 is reflected toward the second traveling body 34 fromthe surface of the original. This light is then further reflected by amirror on the second traveling body 34 so as to pass through animage-forming lens 35 and enter a reading sensor 36. Thus the light isread as image information.

Once the image information has been read in this manner, a drive motorin the printer unit 100, not shown in the drawing, drives one of threesupport rollers 14, 15, 16 to rotate such that the other two supportrollers are driven to rotate thereby. In so doing, the intermediatetransfer belt 10 wrapped around the rollers is caused to perform anendless motion. Laser recording such as that described above and adevelopment process to be described below are also implemented.Monochrome images in black, yellow, magenta, and cyan are then formed onthe photosensitive bodies 40K, Y, M, C as the photosensitive bodies 40K,Y, M, C rotate. These monochrome images are then superposed insuccession at K, Y, M, and C primary transfer nips formed in locationswhere the photosensitive bodies 40K, Y, M, C contact the intermediatetransfer belt 10, and thereby electrostatically transferred to form afour-color superposed toner image. The toner image is then formed on thephotosensitive bodies 40K, 40Y, 40M, 40C.

Meanwhile, the paper feed unit 200 operates one of the three feedrollers such that transfer paper of a size corresponding to the imageinformation is fed, and thus leads the transfer paper to the feed path48 in the printer unit 100. Having entered the feed path 48, thetransfer paper is halted temporarily between the registration rollerpair 49, and then fed at an appropriate timing into the secondarytransfer nip formed at the contact portion between the intermediatetransfer belt 10 and a secondary transfer roller 23 of the secondarytransfer device 22. The four-color superposed toner image on theintermediate transfer belt 10 and the transfer paper are then adheredtogether in synchronization at the secondary transfer nip. Then, as aresult of a transfer electric field formed at the nip, nip pressure, andso on, the four-color superposed toner image is subjected to secondarytransfer onto the transfer paper, where the toner image combines withthe white of the paper to form a full color image.

Having passed through the secondary transfer nip, the transfer paper isconveyed to the fixing device 25 by the endless motion of a conveyorbelt 24 of the secondary transfer device 22. The full color image isthen fixed by the action of pressure applied by a pressure roller 27 ofthe fixing device 25 and heat applied by a heating belt, and then passesdischarge rollers 56 to be discharged onto a paper discharge tray 57provided on the side face of the printer unit 100.

FIG. 2 is an enlarged view showing the constitution of the printer unit100. The printer unit 100 comprises a belt unit, four process units 18K,Y, M, C for forming toner images in each color, the secondary transferdevice 22, a belt cleaning device 17, the fixing device 25, and so on.

The belt unit is caused to perform an endless motion while theintermediate transfer belt 10 wrapped around a plurality of rollers iscaused to contact the photosensitive bodies 40K, Y, M, C. At the K, Y,M, C primary transfer nips where the photosensitive bodies 40K, Y, M, Ccontact the intermediate transfer belt 10, the intermediate transferbelt 10 is pushed toward the photosensitive bodies 40K, Y, M, C from therear surface side thereof by the primary transfer rollers 62K, Y, M, C.A primary transfer bias is applied to the primary transfer rollers 62K,Y, M, C respectively by power sources not shown in the drawing. As aresult, a primary transfer electric field which transfers the tonerimages formed on the photosensitive bodies 40K, Y, M, Celectrostatically toward the intermediate transfer belt 10 is formed atthe K, Y, M, C primary transfer nips. Conductive rollers 74 contactingthe rear surface of the intermediate transfer belt 10 are disposedbetween each of the primary transfer rollers 62K, Y, M, C. Theseconductive rollers 74 prevent the primary transfer bias applied to theprimary transfer rollers 62K, Y, M, C from flowing into the adjacentprocess unit via a medium resistance base layer 11 on the rear surfaceside of the intermediate transfer belt 10.

The process units 18K, Y, M, C are supported on a common carrier as asingle unit comprising the photosensitive bodies 40K, Y, M, C andseveral other devices, and are removable from the print unit 100. Theblack process unit 18K, for example, comprises the photosensitive body40K, and also a developing unit 61K serving as developing means fordeveloping an electrostatic latent image formed on the surface of thephotosensitive body 40K into a black toner image, a photosensitive bodycleaning device 63K for cleaning residual toner adhered to the surfaceof the photosensitive body 40K after passing through the primarytransfer nip, a neutralizing device, not shown in the drawing, forneutralizing the surface of the photosensitive body 40K after cleaning,a charging device, not shown in the drawing, for uniformly charging thesurface of the photosensitive body 40K after neutralization, and soon.Apart from storing toner of different colors, the other color processunits 18K, Y, M, C are constituted substantially identically. In thiscopier, the four process units 18K, Y, M, C are constituted in aso-called tandem form, disposed in series opposing the intermediatetransfer belt 10 in the endless motion direction thereof.

FIG. 3 is a partially enlarged view showing a part of a tandem portion20 comprising the four process units 18K, Y, M, C. Note that apart fromthe color of the toner, the four process units 18K, Y, M, C areconstituted substantially identically, and hence the suffixes K, Y, M, Cattached to each reference numeral have been omitted from the drawing.As shown in the drawing, the process unit 18 comprises a charging device60 serving as charging means, the developing device 61, the primarytransfer roller 62 serving as primary transfer means, the photosensitivebody cleaning device 63, a neutralizing device 64, and so on, disposedaround the photosensitive body 40.

A drum-shaped object constituted by a cylinder made of aluminum or thelike, which is coated with an organic photosensitive material having aphotosensitive property to form a photosensitive layer, is used as thephotosensitive body 40. Note, however, that an object in the form of anendless belt may be used. As the charging device 60, an object which isrotated by causing a charging roller charged with a charging bias tocontact the photosensitive body 40 is used. A scorotron charger or thelike, which performs charging processing in a state of non-contact withthe photosensitive body 40, may be used.

The developing device 61 uses a two-component developer containing amagnetic carrier and a non-magnetic toner to develop latent images. Thedeveloping device 61 comprises an agitating unit 66 which supplies thetwo-component developer stored in the interior of the developing device61 to a developing sleeve 65 by conveying and agitating thetwo-development toner simultaneously, and a developing unit 67 whichtransfers the toner of the two-component developer adhered to thedeveloping sleeve 65 to the photosensitive bodies 40K, Y, M, C.

The agitating unit 66 is provided in a lower position than thedeveloping unit 67, and comprises two screws 68 disposed in parallel, apartition plate provided between the two screws, a toner concentrationsensor 71 provided on the bottom face of a developing case 70, and soon.

The developing unit 67 comprises the developing sleeve 65 opposing thephotosensitive body 40 through an opening in the developing case 70, amagnet roller 72 provided in the interior of the developing sleeve 65 soas to be incapable of rotating, a doctor blade 73, the tip end of whichapproaches the developing sleeve 65, and so on. The gap between thedoctor blade 73 and developing sleeve 65 is set at approximately 500[μm] at its narrowest. The developing sleeve 65 has a sleeve-form whichis capable of non-magnetic rotation. The magnet roller 72, which isconstituted not to rotate with the developing sleeve 65, comprises fivemagnetic poles N1, S1, N2, S2, S3, for example, in the rotary directionof the developing sleeve 65 from the location of the doctor blade 73.These magnetic poles cause magnetic force to act on the two-componentdeveloper on the sleeve in predetermined positions in the rotarydirection. As a result, the two-component developer transmitted from theagitating unit 66 is attracted to and carried on the surface of thedeveloping sleeve 65, and a magnetic brush is formed on the surface ofthe sleeve along the line of magnetic force.

The magnetic brush is restricted to an appropriate layer thickness as itpasses through the opposing position with the doctor blade 73 with therotation of the developing sleeve 65, and is then conveyed to adeveloping region opposite the photosensitive body 40. The magneticbrush is then transferred onto the electrostatic latent image by thepotential difference between the developing bias applied to thedeveloping sleeve 65 and the electrostatic latent image on thephotosensitive body 40, and thus contributes to development. Themagnetic brush is then returned to the developing unit 65 as thedeveloping sleeve 67 continues to rotate, where it is removed from thesurface of the sleeve by the effect of a repulsive magnetic fieldbetween the magnetic poles on the magnetic roller 72, and returned tothe agitating unit 66. In the agitating unit 66, the two-componentdeveloper is replenished with an appropriate amount of toner on thebasis of the detection result of the toner concentration sensor 71. Inthis example, the developing sleeve 65 has a diameter of 18 [mm], andthe surface thereof is subjected to sandblast processing or processingto form a plurality of grooves having a depth of one to several mm suchthat the surface roughness (Rz) is approximately 10 to 30 [μm].

Note that instead of the two-component developer, a single-componentdeveloper which does not contain a magnetic carrier may be employed inthe developing device 61. Further, in this copier the linear speed ofthe photosensitive body 40 is set at 200 [mm/sec], and the linear speedof the developing sleeve 65 is set at 240 [mm/sec]. The diameter of thephotosensitive body 40 is set at 50 [mm], the thickness thereof is setat 30 [μm], the beam spot diameter of the optical system is set at 50×60[μm], and the light quantity is set at 0.47 [mW] The charging potentialV₀ (before exposure) of the photosensitive body 40 is set at −700 [V],the post-exposure potential V_(L) is set at −120 [V], and the developingbias voltage is set at −470 [V]. In other words, development isperformed at a developing potential of 350 [V].

The charging amount of the toner on the developing sleeve 65 ispreferably within a range of −10 to −30 [μC/g]. A developing gap, whichis the gap between the photosensitive body. 40 and developing sleeve 65,may be set within a conventional range of 0.8 to 0.4 [mm], but byreducing this value, the developing efficiency can be improved.

A system whereby a polyurethane rubber cleaning blade 75 is pressedagainst the photosensitive body 40 is used as the photosensitive bodycleaning device 63, but another system may be employed. To improvecleanability, in this example the cleaning device 63 comprises a contactconductive fur brush 76, the outer peripheral surface of which contactsthe photosensitive body 40 and which is rotatable in the direction ofthe arrow in the drawing. A metallic electrostatic roller 77 forapplying a bias to the fur brush 76 is provided rotatably in thedirection of the arrow in the drawing, and the tip end of a scraper 78is pressed against the electrostatic roller 77. The toner that isremoved from the electrostatic roller 77 by the scraper 78 drops onto acollection screw 79 and is thus collected.

The photosensitive body cleaning device 63 constituted in this mannerremoves residual toner from the photosensitive body 40 using the furbrush 76 rotating in a counter direction to the photosensitive body 40.The toner which adheres to the fur brush 76 is removed by theelectrostatic roller 77 which is applied with a bias and rotates in thecounter direction to the fur brush 76 while contacting the fur brush 76.The toner which adheres to the electrostatic roller 77 is cleaned by thescraper 78. The toner which gathers in the photosensitive body cleaningdevice 63 is moved to one side of the photosensitive body cleaningdevice 63 by the collecting screw 79, returned to the developing device61 by a toner recycling device 80, and reused.

The neutralizing device 64 is constituted by a neutralizing lamp or thelike which emits light in order to remove the surface potential of thephotosensitive body 40. Having been neutralized in this manner, thesurface of the photosensitive body 40 is uniformly charged by thecharging device 60, and then subjected to optical recording processing.

The secondary transfer device 22 is provided below the belt unit in thedrawing. The secondary transfer device 22 is caused to perform anendless motion by wrapping the secondary transfer belt 24 around the tworollers 23. One of the two rollers 23 serves as a secondary transferroller that is charged with a secondary transfer bias by a power sourcenot shown in the drawing. This secondary transfer roller 23 sandwichesthe intermediate transfer belt 10 and secondary transfer belt 24 betweenitself and the roller 16 of the belt unit. Thus the two belts move inthe same direction while contacting each other at the contact portion,thereby forming a secondary transfer nip. By means of a secondarytransfer electric field and nip pressure, the four color superposedtoner image on the intermediate transfer belt 10 is subjected tosecondary transfer onto the transfer paper that is conveyed to thesecondary transfer nip from the registration roller pair 49, thusforming a full color image. Having passed through the secondary transfernip, the transfer paper is separated from the intermediate transfer belt10 and carried on the surface of the secondary transfer belt 24 to thefixing device 25 as the belt performs its endless motion. Note thatsecondary transfer may be performed by a transfer charger or the likeinstead of the secondary transfer roller.

After passing through the secondary transfer nip, the surface of theintermediate transfer belt 10 reaches the support position of thesupport roller 15. Here, the intermediate transfer belt 10 is interposedbetween the belt cleaning device 17 which contacts the front surface(outer loop surface) of the belt, and the support roller 15 whichcontacts the rear surface. The residual toner adhered to the frontsurface is removed by the belt cleaning device 17, whereupon the beltenters the K, Y, M, C primary transfer nips in succession so that thenext four color toner image can be superposed.

The belt cleaning device 17 comprises two fur brushes 90, 91 as cleaningmembers. These fur brushes 90, 91 each have a diameter of 20 [mm], areconstituted by a plurality of acrylic carbon filaments filled into arotary core at a density of 6.25 [D/F, 100,000/inch²], and exhibit anelectric resistance of approximately 1×10⁷ [Ω]. The fur brushes 90, 91wipe residual toner from the belt mechanically by having the pluralityof filaments rotate in a counter direction to the filling direction ofthe filaments while contacting the intermediate transfer belt 10. Thewiped residual toner is also attracted electrostatically and collectedby applying a cleaning bias using a power source not shown in thedrawing.

Metallic rollers 92, 93 rotate in a forward direction or reversedirection to the fur brushes 90, 91 while contacting the fur brushes 90,91 respectively. Of the two metallic rollers 92, 93, a negative voltageis applied to the metallic roller 92 positioned at the upstream side inthe direction of rotation of the intermediate transfer belt 10 by apower source 94, whereas a positive voltage is applied to the metallicroller 93 positioned at the downstream side by a power source 95. Thetip ends of blades 96, 97 contact the metallic rollers 92, 93respectively. By means of this constitution, while the intermediatetransfer belt 10 performs an endless motion in the direction indicatedby an arrow in the drawing, the upstream side fur brush 90 cleans thesurface of the intermediate transfer belt 10. At this time, if −700 [V],for example, are applied to the metallic roller 92 and −400 [V] areapplied to the fur brush 90, first the positive polarity toner on theintermediate transfer belt 10 is transferred electrostatically to thefur brush 90 side. The toner transferred to the fur brush side is thentransferred to the metallic roller 92 from the fur brush 90 due to thepotential difference, and is scraped off by the blade 96.

A lot of toner is left on the intermediate transfer belt 10 even afterthe fur brush 90 has removed the toner from the intermediate transferbelt 10 in the manner described above. This toner is charged to negativepolarity by the negative bias applied to the fur brush 90. This chargingis assumed to be performed by charge injection or discharge. Next, thedownstream fur brush 91 is used to perform cleaning by applying apositive bias, and thus the remaining toner can be removed. The removedtoner is transferred to the metallic roller 93 from the fur brush 91 bythe potential difference, scraped off by the blade 97, and collected ina tank not shown in the drawing.

Although most of the toner is removed from the surface of theintermediate transfer belt 10 by this cleaning performed by the furbrush 91, a little toner still remains. The remaining toner on theintermediate transfer belt 10 is charged to a positive polarity by thepositive bias applied to the fur brush 91 as described above. This toneris transferred to the side of the photosensitive bodies 40K, Y, M, C bya transfer electric field applied at the primary transfer position, andcollected by the photosensitive body cleaning device 63.

Although the registration roller pair 49 is, in many cases, grounded, abias may be applied in order to remove paper particles of the transferpaper P. A conductive rubber roller, for example, is used to apply thebias. The roller may have a diameter of 18 [μm], and be covered withconductive NBR rubber having a thickness of 1 [μm]. The electricresistance is equivalent to the volume resistivity of the rubbermaterial, and hence approximately 10×10⁹ [Ω×cm]. A voltage of about −800[V] is applied to the side (front side) on which the toner istransferred. A voltage of about +200 [V] is applied to the rear surfaceside of the paper.

Generally, in the intermediate transfer system, paper particles cannoteasily move to the photosensitive bodies, and hence the intermediatetransfer system may be grounded without taking paper particle transfergreatly into account. The voltage is generally applied as a DC bias, butmay be applied as an AC voltage containing a DC offset component inorder to charge the transfer paper P more evenly. Thus the papersurface, having passed through the registration roller pair 49 appliedwith a bias in this manner, is charged slightly to the negative side.Accordingly, during transfer from the intermediate transfer belt 10 tothe transfer paper P, the transfer conditions may vary from those whenno voltage is applied to the registration roller pair 49.

Note that in this embodiment, a transfer paper turning device 28 (seeFIG. 1) is provided below the secondary transfer device 22 and fixingdevice 25 in parallel with the aforementioned tandem portion 20. Thusthe transfer paper, having finished image fixing processing on one side,is turned over using a switching claw to switch the path of the transferpaper to the transfer paper turning device side, and returned to thesecondary transfer nip. Secondary transfer processing and fixingprocessing are then implemented on the image on the other side of thetransfer paper, whereupon the transfer paper is discharged onto thepaper discharge tray.

This copier comprises information obtaining means for obtaining variousinformation relating to the state of the constitutional components ofthe copier and phenomena occurring in the interior of the copier. Theseinformation obtaining means are constituted by a control unit 1, varioussensors 2, an operation display device 3, and so on, shown in FIG. 4.The control unit 1 serves as control means for controlling the entirecopier, and comprises ROM 1 c serving as information storage meansstoring a control program, RAM 1 b serving as information storage meansfor storing calculation data, control parameters, and the like, a CPU 1a serving as calculation means, and so on. The operation display unit 3comprises a display unit 3 a constituted by a liquid crystal display orthe like for displaying written information and the like, an operatingunit 3 b for receiving input information from an operator through akeypad or the like, and transmitting this input information to thecontrol unit 1, and so on. In this copier, the information obtainingmeans constituted by the control unit 1, various sensors 2, operationdisplay unit 3, and so on function as an abnormality determiningapparatus comprising determining means for determining an abnormality inthe detection subject copier on the basis of the stored informationstored in the information storage means such as the ROM 1 c and variousinformation obtained by the obtaining function of the informationobtaining means itself.

The information that is obtained by the information obtaining means ofthis copier includes sensing information, control parameter information,input information, image reading information, and so on. Thisinformation will now be described in detail.

(a) Sensing Information

The items that may be obtained as sensing information include drivingrelationships, various characteristics of the recording medium,developer characteristics, photosensitive body characteristics, variouselectrophotographic processing states, environmental conditions, andvarious characteristics of the recorded object. This sensing informationwill be described in outline below.

(a-1) Driving Information Includes:

detecting the rotation speed of the photosensitive drum using anencoder, reading the current value of the drive motor, reading thetemperature of the drive motor;

similarly detecting the driving state of cylindrical or belt-form rotarycomponents such as the fixing rollers, paper conveyance rollers, anddrive rollers; and

detecting sound generated by driving using a microphone installed in theinterior of the device or outside of the device.

(a-2) Paper Conveyance Conditions Include:

reading the position of the front end/rear end of the conveyed paperusing a transmission type or reflection type optical sensor, or acontact type sensor, detecting the occurrence of a paper jam, andreading deviations in the transmission timing of the front end/rear endof the paper, or variation in a perpendicular direction to theconveyance direction;

similarly determining the traveling speed of the paper by means of thedetection timing of a plurality of sensors; and

determining slippage between the feed roller and the paper during paperfeeding by comparing a measured value of the roller rotation speed andthe travel of the paper.

(a-3) Various Characteristics of a Recording Medium Such as Paper

This information greatly affects the image quality and sheet conveyancestability. The following methods are used to obtain information relatingto the paper type.

The paper thickness is determined by fixing the paper between tworollers and detecting relative positional displacement of the rollersusing an optical sensor or the like, or detecting an equal displacementto the travel of a member that is pushed upward when the paper isintroduced.

The surface roughness of the paper is determined by causing a guide orthe like to contact the surface of the paper prior to transfer, anddetecting the oscillation, sliding sound, or the like produced by thiscontact.

The gloss of the paper is determined by irradiating luminous flux of aprescribed angle of aperture at a prescribed angle of incidence, andmeasuring the luminous flux of a prescribed angle of aperture that isreflected in a specular reflection direction using a sensor.

The rigidity of the paper is determined by detecting the amount ofdeformation (curvature) of a pressed piece of paper.

A determination as to whether or not the paper is recycled paper isperformed by irradiating the paper with ultraviolet light and detectingits transmittivity.

A determination as to whether or not the paper is backing paper isperformed by irradiating the paper with light from a linear light sourcesuch as an LED array, and detecting the light reflected from thetransfer surface using a solid state imaging element such as a CCD.

A determination as to whether or not the paper is OHP paper is performedby irradiating the paper with light, and detecting regular reflectionlight having a different angle to that of the transmitted light.

The moisture content of the paper is determined by measuring theabsorption of infrared light or μ wave light.

The curl is detected using an optical sensor, contact sensor, orsimilar.

The electric resistance of the paper is determined by causing a pair ofelectrodes (feed rollers or the like) to contact the recording paper andmeasuring the electric resistance directly, or measuring the surfacepotential of the photosensitive body or intermediate transfer bodyfollowing transfer, and estimating the resistance value of the recordingpaper from the measured value.

(a-4) Developer Characteristics

The characteristics of the developer (toner/carrier) in the devicefundamentally affect the electrophotographic process function, and aretherefore an important factor in the operation and output of the system.It is vital to obtain information regarding the developer. The followingitems may be cited as examples of developer characteristics.

Regarding the toner, the charging amount and distribution, fluidity,cohesion, bulk density, electric resistance, external additive amount,consumption amount or remaining amount, fluidity, and tonerconcentration (mixing ratio of toner and carrier) may be cited ascharacteristics.

Regarding the carrier, the magnetic property, coating thickness, spentamount, and so on may be cited as characteristics.

It is usually difficult to detect items such as those described aboveindividually in the interior of the image forming apparatus. Therefore,an overall characteristic of the developer is detected. The overallcharacteristic of the developer may be measured in the following ways,for example.

A test latent image is formed on the photosensitive body, developedunder predetermined developing conditions, and the reflection density(optical reflectance) of the formed toner image is measured.

A pair of electrodes is provided in the developing device, and therelationship between the applied voltage and current (resistance,permittivity, and so on) is measured.

A coil is provided in the developing device, and the voltage-currentcharacteristic (inductance) is measured.

A level sensor is provided in the developing device, and the developervolume is detected. The level sensor may be an optical sensor, acapacitance sensor, or similar.

(a-5) Photosensitive Body Characteristics

Similarly to the developer characteristics, the photosensitive bodycharacteristics relate closely to the electrophotographic processfunction. Examples of information regarding the photosensitive bodycharacteristics include the photosensitive film thickness, the surfacecharacteristics (coefficient of friction, irregularities), surfacepotential (before and after each process), surface energy, scatteredlight, temperature, color, surface position (deflection), linear speed,potential attenuation speed, resistance/capacitance, surface moisturecontent, and so on. From among these examples, the following informationcan be detected within the image forming apparatus.

Variation in the capacitance accompanying film thickness variation canbe detected by detecting the current flowing from a charging member tothe photosensitive body, and simultaneously comparing the voltageapplied to the charging member with the voltage-current characteristicrelating to a preset dielectric thickness of the photosensitive body todetermine the film thickness.

The surface potential and temperature can be determined by a well-knownsensor.

The linear speed is detected by an encoder or the like attached to arotary shaft of the photosensitive body.

Scattered light from the surface of the photosensitive body is detectedby an optical sensor.

(a-6) State of the Electrophotographic Process

As is well-known, toner image formation through electrophotography isperformed by a succession of processes comprising: uniform charging ofthe photosensitive body; latent image formation (image exposure) bymeans of laser light or the like; development using toner (coloringparticles) carrying an electric charge; transfer of the toner image ontoa transfer material (in the case of a color image, this is performed bysuperposing toner onto an intermediate transfer body or the recordingmedium, which is the final transfer body, or by means of superpositiondevelopment onto the photosensitive body during development); and fixingof the toner image on the recording medium. The various information ateach of these stages greatly affects the image and other system output.It is important to obtain this information in order to evaluate thestability of the system. Specific examples of ways in which informationrelating to the state of the electrophotographic process is obtained areas follows:

the charging potential and exposure unit potential are detected by awell-known surface potential sensor;

the gap between the charging member and photosensitive body duringnon-contact charging is detected by measuring the amount of lightpassing through the gap;

the electromagnetic wave caused by charging is perceived by a widebandantenna;

the sound generated by charging;

the exposure intensity; and

the exposure optical wavelength.

Further, the following can be cited as methods of obtaining variousstates of the toner image.

The pile height (height of the toner image) is detected by measuringdepth from the vertical direction using a displacement sensor, andmeasuring shielding length from the horizontal direction using aparallel ray linear sensor.

The toner charging amount is measured by a potential sensor whichmeasures the potential of an electrostatic latent image on a solidportion and the potential when the latent image has been developed, anddetermined from the ratio thereof to an adhesion amount calculated by areflection density sensor in the same location.

Dot fluctuation or scattering is determined by detecting a dot patternimage using an infrared light area sensor on the photosensitive body andarea sensors of wavelengths corresponding to each color on theintermediate transfer body, and then implementing appropriateprocessing.

The offset amount (after fixing) is read by optical sensors in locationscorresponding to the surface of the recording-paper and the surface ofthe fixing roller respectively, and determined by comparing the twoobtained sensor values.

The remaining transfer amount is determined by disposing optical sensorsafter the transfer step (on the PD and the belt) and measuring theamount of reflected light from the remaining transfer pattern followingthe transfer of a specific pattern.

Color unevenness during superposition is detected by a full color sensorwhich detects the surface of the recording paper following fixing.

(a-7) Formed Toner Image Characteristics

Image density and color are detected optically (by either reflectedlight or transmitted light; the projection wavelength is selectedaccording to the color). To obtain density and single color information,this detection may be performed on the photosensitive body orintermediate transfer body, but to measure a color combination, such ascolor unevenness, the detection must be performed on the paper.

Gradation is determined using an optical sensor by detecting thereflection density of a toner image formed on the photosensitive body ora toner image transferred onto a transfer body at each gradation level.

Definition is detected using a monocular sensor with a small spotdiameter or a high resolution line sensor by reading a developed ortransferred image to determine a repeated line pattern.

Graininess (roughness) is determined by the same method used to detectthe definition, by reading a halftone image and calculating the noisecomponent.

Registration skew is determined by providing an optical sensor at eachend of the main scanning direction following registration, and measuringthe difference between the ON timing of the registration rollers and thedetection timing of the two sensors.

Mis-color registration is determined by detecting the edge portions of asuperposed image on the intermediate transfer body or recording paperusing a monocular small-diameter spot sensor or a high resolution linesensor.

Banding (density unevenness in the conveyance direction) is detected bymeasuring density unevenness in the sub scanning direction on thetransfer paper using a small-diameter spot sensor or a high resolutionline sensor, and measuring the signal quantity at a specific frequency.

Glossiness (unevenness) is detected by providing apiece of recordingpaper formed with a uniform image so as to be scanned by a regularreflection-type optical sensor.

Fogging is detected using a method of reading an image backgroundportion using an optical sensor for scanning a comparatively wide regionon the photosensitive body, intermediate transfer body, or recordingpaper, or a method of obtaining image information for each area of thebackground region using a high resolution area sensor, and counting thenumber of toner particles in the image.

(a-8) Physical Characteristics of Printed Objects in the Image FormingApparatus

Image deletion/fading and so on is determined by scanning a toner imageon the photosensitive body, intermediate transfer body, or recordingpaper using an area sensor, and subjecting the obtained imageinformation to image processing.

Scattering is determined by scanning an image on the recording paperusing a high resolution line sensor or an area sensor, and calculatingthe amount of toner scattered around the periphery of the patternportion.

Rear end blank spots and bet across blank spots are detected by a highresolution line sensor on the photosensitive body, intermediate transferbody, or recording paper.

Curling, rippling, and folding are detected by a displacement sensor. Itis effective to dispose a sensor in a location near to the two end partsof the recording paper to detect folding.

Contamination and flaws on the cross-cut surface are detected by an areasensor provided vertically in the paper discharge tray by capturing animage of and analyzing the cross-cut surface when a certain amount ofdelivered paper has accumulated.

(a-9) Environmental Conditions

To detect temperature, a thermocouple system which extracts as a signala thermoelectromotive force generated at a contact point joining twodifferent metals or a metal and a semiconductor, a resistivity variationelement using temperature-based variation in the resistivity of a metalor semiconductor, a pyroelectric element in which, with a certain typeof crystal, the charge in the crystal is polarized with an increase intemperature to generate a surface potential, a thermomagnetic effectelement which detects change in the magnetic property according totemperature, and so on may be employed.

To detect humidity, an optical measurement method for measuring theoptical absorption of H₂O or an OH group, a humidity sensor whichmeasures variation in the electric resistance value of a material due towater vapor adsorption, and so on may be employed.

Various gases are detected by measuring change in the electricresistance of an oxide semiconductor basically accompanying gasadsorption.

To detect airflow (direction, flow speed, gas type), an opticalmeasurement method or the like may be used, but an air-bridge type flowsensor which, due to its small size, enables a reduction in the size ofthe system, is particularly useful.

To detect air pressure and pressure, methods such as using a pressuresensitive material to measure the mechanical displacement of a membranemay be employed. Similar methods may be used to detect oscillation.

(b) Regarding Control Parameter Information

An operation of the image forming apparatus is determined by the controlunit, and hence it is effective to use the input/output parameters ofthe control unit directly.

(b-1) Image Formation Parameters

These are direct parameters output as a result of calculation processingperformed by the control unit for the purpose of image formation, suchas the following:

set values of the process conditions set by the control unit, forexample the charging potential, developing bias value, fixingtemperature set value, and so on;

similarly, set values of various image formation parameters for halftoneprocessing, color correction, and so on;

various parameters set by the control unit to operate the device, forexample the paper conveyance timing, the execution period of apreparatory mode prior to image formation, and so on.

(b-2) User Operating History

The frequency of various operations selected by the user, such as thenumber of colors, number of sheets, image quality instructions, and soon.

The frequency of paper size selections by the user.

(b-3) Power Consumption

The total power consumption over the entire period or a specific timeunit (one day, one week, one month, etc.), or the distribution,variation (derivative), and cumulative value (integral) thereof.

(b-4) Information Regarding Consumption of Consumables

Usage of the toner, photosensitive body, and paper over the entireperiod or a specific time unit (one day, one week, one month, etc.), orthe distribution, variation (derivative), and cumulative value(integral) thereof.

(b-5) Information Regarding the Occurrence of a Fault

The frequency with which a fault occurs (by type) over the entire periodor a specific time unit (one day, one week, one month, etc.), or thedistribution, variation (derivative), and cumulative value (integral)thereof.

(c) Input Image Information

The following information can be obtained from image informationtransmitted from a host computer as direct data or image informationobtained after being read from an original image by a scanner andsubjected to image processing.

The cumulative number of color pixels is determined by counting imagedata by GRB signal for each pixel.

Using a method such as that described in Japanese Patent Publication No.2621879, for example, an original image can be divided into characters,halftone dots, photographs, and background, and thus the ratio of thecharacter portion, halftone portion, and so on can be determined. Theratio of colored characters can be determined in a similar manner.

By counting the cumulative value of the color pixels in each of aplurality of regions partitioned in the main scanning direction, thetoner consumption distribution in the main scanning direction can bedetermined.

The image size is determined according to image size signals generatedby the control unit or the distribution of color pixels in the imagedata.

The character type (size, font) is determined from attribute data of thecharacters.

The various information cited above can be obtained by well-knowntechniques in a typical image forming apparatus. The informationobtaining means of the copier described up to this point are capable ofobtaining at least the information described in the following sections(1) to (12).

(1) Temperature

The copier comprises a temperature sensor using a resistance variationelement to obtain temperature information due to the simple principlesand constitution of the resistance variation element and the possibilityof reducing the element to an extremely small size. FIG. 5 is aperspective view showing a thin film-type resistance variation elementin this temperature sensor. The resistance variation element may beconstructed as follows. First, a dielectric film 502 is formed on asubstrate 501, and then a thin film-form sensor unit 503 constituted bya metallic or semiconductor material is provided thereabove. Padelectrodes 504 are provided at each end of the sensor unit 503, andfinally, a lead wire 505 is connected to the pad electrodes 504. In thisresistance variation element, the electric resistance of the sensor unit503 varies with a variation in the ambient temperature, and thisvariation may be derived as a variation in voltage or current. Since thesensor unit 503 is a thin film, the entire element can be reduced insize, and is therefore easy to incorporate into the system.

FIG. 6 is a perspective view showing a resistance variation elementhaving a different constitution to that shown in FIG. 5. This resistancevariation element differs from the resistance variation element shown inFIG. 5 in that the thin film-form sensor unit 503 is disposed on a thinfilm bridge 507 which is suspended in midair and separated from thesubstrate 501 via a spacer 506. By means of such a constitution, heatdissipation from the sensor unit 503 is prevented, and theresponsiveness of the sensor unit 503 to temperature is improved. Withthis constitution, it is possible to detect only radiation heat from themeasured portion, which is favorable during non-contact measurement.

(2) Humidity

A humidity sensor which can be reduced to a small size is useful. Thebasic principle thereof is that when water vapor is adsorbed to amoisture-sensitive ceramic, ion conduction is increased by the adsorbedwater such that the electric resistance of the ceramic decreases. Themoisture-sensitive ceramic material is a porous material such as analumina-based ceramic, apatite-based ceramic, ZrO₂—MgO based ceramic, orsimilar. FIG. 7 is a perspective view showing a humidity sensorinstalled in the copier. A comb-shaped electrode 512 is provided on aninsulating substrate 511, and terminals 513 are connected to each endthereof. A moisture-sensitive layer 514 (typically, a moisture-sensitiveceramic) is provided and the entire sensor is covered by a case 515.When water vapor is adsorbed to the moisture-sensitive ceramic throughthe case 515, the electric resistance falls, and this may be measured asvoltage or current variation.

(3) Oscillation

The oscillation sensor is basically the same as a sensor which measuresair pressure and pressure, and a sensor using silicon, which can bereduced to an extremely small size and installed in the system easily,is particularly useful. The motion of an oscillator manufactured on athin silicon diaphragm can be measured by measuring volumetric changebetween the oscillator and a counter electrode provided opposite theoscillator, or using the piezoresistance effect of the Si diaphragmitself. FIG. 8 is a sectional view showing an oscillation sensorinstalled in the copier. A counter electrode 522 is provided on aninsulating substrate 521. Next, a thin diaphragm 524 and an oscillator525 are provided on a silicon substrate 523. A stepped portion 526 isthen formed to maintain the gap with the counter electrode 522, andjoined to the substrate 521 comprising the counter electrode 522 formedin advance. When peripheral oscillation or pressure is applied to thesensor in this state, the oscillator 525 begins to oscillate, and thismay be measured as volumetric change between the oscillator 525 and thecounter electrode 522.

(4) Toner Concentration (for Four Colors)

The toner concentration is detected for each color. A known sensor maybe used as the toner concentration sensor. For example, the tonerconcentration may be detected using a sensing system disclosed inJapanese Unexamined Patent Application Publication H6-289717, whichmeasures variation in the magnetic permeability of the developer in adeveloping device. FIG. 9 is a schematic diagram showing theconstitution of a concentration detection unit of a toner concentrationsensor installed in this copier. For example, a reference coil 533 isconnected differentially to a detection coil 532 disposed in thevicinity of a developer 531 formed from a mixture of a magnetic carrierand a non-magnetic toner. The inductance of the detection coil 532varies in accordance with variation in the magnetic permeability causedby an increase or decrease in the toner concentration (directly, in themagnetic carrier), whereas the inductance of the reference coil 533 isnot affected by variation in the toner concentration. An alternatingcurrent drive source 534 which oscillates at 500 [kHz], for example, isconnected to the series circuit constituted by the two coils 532, 533 soas to drive the two coils 532, 533. A differential output is derivedfrom the connection point of the two coils 532, 533, and this output isconnected to a phase comparator 535. One of the outputs of thealternating current drive source 534 is connected separately to thephase comparator 535, and thus the phase of the voltage and differentialoutput voltage from the drive source 534 are compared. A sensitivitysetting resistance 536 (R1) is connected in series with at least one ofthe detection coil S32 and the reference coil 533 (the detection coil532 in the illustrated example) in order to increase sensitivity tovariation in the toner concentration, thereby enabling control of thesensitivity characteristic. An assembly drawing of the two coils isshown in FIG. 10. The two coils 532, 533 are wound on a tubular coilsupport 537 adjacent to each other in the vertical direction of thedrawing. The detection coil 532 is positioned on the side nearest thedeveloper 531 in order to detect variation in the magnetic permeability,and the reference coil 533 is disposed on the far side so that themagnetic permeability does not change even when the toner concentrationvaries.

(5) Photosensitive Body Uniform Charging Potential (for Four Colors)

The uniform charging potential is detected in the photosensitive bodies40K, Y, M, C of each color. FIG. 11 is a schematic diagram showing theconstitution of a potential measuring system installed in the copier. Inthe drawing, the reference numeral 541 denotes a sensor unit substrateattached opposite a physical object (not shown). The reference numeral542 denotes a signal processing unit substrate for transmitting drivesignals to and receiving sensor output from the sensor unit substrate541. A tuning fork 543 serving as chopping means and a piezoelectricelement 544 are provided within the sensor unit substrate 541. Thepiezoelectric element 544 is driven by a drive signal from the signalprocessing unit substrate 542. In this potential measuring system, aself-oscillation system loop is used such that when one piezoelectricelement 544 is driven, the resulting oscillation is transmitted toanother piezoelectric element 544 a through the tuning fork 543, andthen returns to the drive source. The reference numeral 545 denotes ameasuring electrode (to be referred to as “electrode” hereafter) whichreceives an electric line of force from the physical object. Thereference numeral 546 denotes an amplifier which amplifies the temporalvariation in the electric line of force S received by the electrode 545.

A piezoelectric element drive circuit 547, a filter 548, and apiezoelectric element drive circuit 549 are provided in the signalprocessing unit substrate 542. The filter 548 shapes a waveform. Thephase-shift circuit 549 aims to shift the phase difference between thedrive signal fed into the sensor and the actual drive signal by 180° sothat they cancel each other out. The phase difference between the twosignals typically differs according to the feed path. An attenuator 550serves to adjust the size of a phase-adjusted correction signal. Anadding circuit 551 adds the correction signal to the sensor output. Aprocessing circuit 552 processes the final signal output, and thusdetermines the potential of the physical object. The reference numerals553, 554 denote a phase-shift circuit and an attenuator adjusting volumerespectively. With this constitution, the phase-shift and attenuatorgain are optimized such that an opposite phase and a signal of the samelevel can be added as a correction signal, thus enabling only sensoroutput based on the actual physical object to be detected. Further, byproviding adjustment means, characteristic variation accompanying changeover time can be dealt with by means of adjustment, and thus thereliability of the sensor is improved.

(6) Post-Development Potential of Photosensitive Body (for Four Colors)

The surface potential of the photosensitive bodies 40K, Y, M, Cfollowing optical recording is detected in the same manner as thatdescribed in (5).

(7) Colored Area Ratio (for Four Colors)

The colored area ratio is determined for each color from the ratio ofthe total cumulative value of the pixels to be colored and the totalcumulative value of all of the pixels, which is learned from the inputimage information.

(8) Development Toner Amount (for Four Colors)

The toner adhesion amount per unit area on each of the toner imagesdeveloped on the photosensitive bodies 40K, Y, M, C is determined on thebasis of the optical reflectance produced by a reflection photosensor.The reflection photosensor irradiates a physical object with LED light,and detects the reflected light using a light-receiving element. Acorrelative relationship is established between the toner adhesionamount and the optical reflectance, and hence the toner adhesion amountcan be determined on the basis of the optical reflectance.

(9) Slanting of Paper Front End Position

A pair of optical sensors is disposed at a point on the paper feed pathfrom the feed roller of the paper feed unit 200 to the secondarytransfer nip in order to detect the transfer paper at both ends of anorthogonal direction to the conveyance direction, and thus the two endsof the conveyed transfer paper in the vicinity of the front end thereofare detected. The two optical sensors are used to measure the timerequired for the paper to pass through, using the time at which a feedroller drive signal is issued as a reference, and slanting of thetransfer paper in relation to the conveyance direction is determined onthe basis of a divergence in this time.

(10) Paper Discharge Timing

The transfer paper is detected by an optical sensor after passingthrough a pair of discharge rollers (56 in FIG. 1). Similarly in thiscase, measurement is performed with the time at which the feed rollerdrive signal is issued as a reference.

(11) Photosensitive Body Total Current (for Four Colors)

The current flowing out to earth from the photosensitive bodies 40K, Y,M, C is detected. This current can be detected by providing currentmeasuring means between the photosensitive body substrate and the groundterminal.

(12) Drive Power of Photosensitive Body (for Four Colors)

The drive power (current×voltage) consumed by the drive source (motor)of the photosensitive bodies during driving is detected by an ammeter, avoltmeter, and so on.

Next, the characteristic constitution of this copier will be described.

The copier is designed to determine whether or not an abnormality hasoccurred in the apparatus by determining a Mahalanobis distance using anMTS method on the basis of grouped information constituted by aplurality of types of information obtained by the information obtainingmeans. To implement this determination, an inverse matrix of a normalgroup data set obtained in advance is stored in the ROM 1 c of thecontrol unit 1. The CPU 1 a determines on the basis of this inversematrix whether or not an abnormality is present in the groupedinformation comprising all or some combinations of the variousinformation obtained by the information obtaining means, and thendisplays fault warning information on the operation display unit 3 inaccordance with the result. In other words, in this copier the controlunit 1 functions as determining means for determining the presence of anabnormality in the detection subject copier. Note that a notificationmethod using sound, characters, a lamp display, and so on, instead ofdisplay on the operation display unit 3, may be employed as notificationmeans for notifying the user of the fault warning information.

FIG. 17 is an obtained data table illustrating a normal data obtainingprocess performed to construct the inverse matrix described above on thebasis of the various information obtained from the copier in a normalstate. In this obtained data table, an example is illustrated in whichthe inverse matrix is constructed from n sets of grouped informationcomprising k types of information.

In the normal data obtaining process, first, k types of information y₁₁,y₁₂, . . . , y_(1k), constituting a first set of grouped information,are obtained respectively by the information obtaining means, and storedin information storage means such as RAM of a test machine as data onthe first row of the data table. Next, k types of information y₂₁, y₂₂,. . . , y_(2k), constituting a second set of grouped information, areobtained respectively by the information obtaining means, and stored inthe information storage means as data on the second row of the datatable. The third set to the nth set of grouped information are thenobtained similarly and stored in the information storage means as dataon the third row to the nth row of the data table. Finally, the averageand standard deviation a of the respective n sets are determined for thek types of information constituting each set of grouped information andstored in the information storage means as data on the n+1 and n+2 rowsrespectively.

Once the normal data obtaining process is complete, an informationnormalization process is implemented to construct a normalized datatable such as that shown in FIG. 18. This normalized data table isconstructed on the basis of the obtained data table described above.

Data normalization refers to processing for transforming the absolutevalue information of the obtained information into variable information.The normalized data of the various information is calculated on thebasis of the following Eq. (1). Note that in the following expression,the symbol i denotes any one of the n sets of grouped information, andthe symbol j denotes any one of the k types of information.Y _(ij)=(y _(ij) − y_(j) )/σ _(j)  Eq. (1)

Once this information normalization process is complete, a correlationcoefficient calculation process is performed. In the correlationcoefficient calculation process, a correlation coefficient r_(pq)(r_(pq)) is calculated on the basis of the following Eq. (2) for allpossible combinations (_(k)C₂ variants) of two different types of the ktypes of normalized data in the n groups of normalized data sets.

$\begin{matrix}{r_{pq} = {r_{qp} = \frac{\sum\limits_{i = 1}^{n}\;\left( {Y_{ip} \times Y_{iq}} \right)}{\sqrt{\sum\limits_{i = 1}^{n}\;{\left( Y_{ip} \right)^{2} \times {\sum\limits_{i = 1}^{n}\;\left( Y_{iq} \right)^{2}}}}}}} & {{Eq}.\mspace{14mu}(2)}\end{matrix}$

When the correlation coefficient r_(pq) (r_(pq)) has been calculated forall of the combinations, a k×k correlation coefficient matrix R isconstructed with 1 as its diagonal element and the correlationcoefficient r_(pq) as the remaining elements of the p rows and qcolumns. The content of the correlation coefficient matrix R is as shownin Eq. (3).

$\begin{matrix}{R = \begin{pmatrix}1 & r_{12} & r_{13} & \cdots & r_{1k} \\r_{21} & 1 & r_{23} & \cdots & r_{2k} \\r_{31} & r_{32} & 1 & \cdots & r_{3k} \\\cdots & \cdots & \cdots & \cdots & \cdots \\r_{k1} & r_{k2} & r_{k3} & \cdots & 1\end{pmatrix}} & {{Eq}.\mspace{14mu}(3)}\end{matrix}$

Once this correlation coefficient calculation process is complete, amatrix transformation process is implemented. By means of this matrixtransformation process, the correlation coefficient matrix R shown inEq. (3) is transformed into an inverse matrix A (R⁻¹) shown in Eq. (4).

$\begin{matrix}{A = {\begin{pmatrix}a_{11} & a_{12} & a_{13} & \cdots & a_{1k} \\a_{21} & a_{22} & a_{23} & \cdots & a_{2k} \\a_{31} & a_{32} & a_{33} & \cdots & a_{3k} \\\cdots & \cdots & \cdots & \cdots & \cdots \\a_{k1} & a_{k2} & a_{k3} & \cdots & a_{kk}\end{pmatrix} = R^{- 1}}} & {{Eq}.\mspace{14mu}(4)}\end{matrix}$

In this copier, the inverse matrix A constructed by the series ofprocesses described above, comprising the normal data obtaining process,the information normalization process, the correlation coefficientcalculation process, and the matrix transformation process, is stored inthe ROM 1 c. Then, the Mahalanobis distance D on the multidimensionalspace produced by the inverse matrix A is calculated on the basis of Eq.(5) for the grouped information constituted by all or some combinationsof the various information obtained periodically by the informationobtaining means.

$\begin{matrix}{D^{2} = {\frac{1}{k}{\sum\limits_{P = 1}^{k}\;{\sum\limits_{q = 1}^{k}\;{a_{pq}Y_{p}Y_{q}}}}}} & {{Eq}.\mspace{14mu}(5)}\end{matrix}$

FIG. 12 is a flowchart showing the series of processes from the normaldata obtaining process to the matrix transformation process. In theflowchart, first n groups of k pieces of information relating to thestate of the copier are obtained while the copier is operative (step1-1: hereafter, step will be abbreviated to S). Next, an average valueand standard deviation σ are calculated on the basis of the above Eq.(1) for each type (j) of information, and a normalized data table isconstructed from the calculation results (S1-2). The correlationcoefficient matrix R is then constructed on the basis of the normalizeddata table (S1-3), and then transformed into the inverse matrix A(S1-4).

FIG. 13 is a flowchart showing a procedure for calculating theMahalanobis distance D on the basis of the inverse matrix A and thevarious obtained data. In this procedure, first k types of data x₁, x₂,. . . , x_(k) in any state are obtained (S2-1). The data typescorrespond to Y₁₁, y₁₂, . . . , y_(1k), and so on. Next, the obtaineddata are normalized respectively to X₁, X₂, . . . , X_(k) on the basisof Eq. (1) above. Then, using Eq. (5) above, which is determined usingthe element a_(kk) of the constructed inverse matrix A, the square ofthe Mahalanobis distance D is calculated. The symbol Σ in the drawingdenotes the sum relating to the suffixes p and q.

The control unit 1 compares the Mahalanobis distance D determined inthis manner to a preset threshold. When the Mahalanobis distance D isgreater than the threshold, the control unit 1 determines the obtainedgrouped information to be abnormal data deviating greatly from a normaldistribution, and hence displays fault warning information on theoperation display unit 3.

An example in which the inverse matrix A serving as a normal group dataset is stored in the ROM 1 c was described, but the normal group dataset may be stored as the aforementioned obtained data table storing thevarious information obtained in the normal data obtaining process, theaforementioned normalized data table, the aforementioned correlationcoefficient matrix R, and so on instead of the inverse matrix A. Whenone of these normal group data sets is stored instead of the inversematrix A, the inverse matrix A should be constructed on the basis of thedata prior to abnormality determination.

According to the copier constituted in this manner, the presence of anabnormality in the obtained results of the grouped informationconstituted by all or some combinations of various information isdetermined using an MTS method, and hence various types of abnormalitycan be discovered in a wide range. Moreover, since there is no need tomonitor the presence of the causes of each individual abnormality, anincrease in control complexity caused by such monitoring can be avoided.However, it is difficult to specify the type of abnormality when anabnormality is discovered in a test copier on which this type ofabnormality determination is performed.

Hence in this copier, abnormality types are divided into severalcategories, and the grouped information required to determine theindividual abnormalities within the categories is obtained for eachcategory. Mahalanobis distances D are then determined respectively onthe basis of the obtained results and the inverse matrix A serving asthe corresponding normal group data set.

FIG. 19 is a table showing an example of a relationship betweencategories of abnormality types in the copier, and the groupedinformation required to determine an abnormality within thesecategories.

In FIG. 19, an example is shown in which abnormalities relating to threecategories are determined respectively on the basis of the 12 items and33 types (5 items+7 items×four colors) of obtained information from theaforementioned (1) temperature to (12) drive power of photosensitivebody. As shown in the drawing, for an abnormality relating to a paperjam, a determination can be made on the basis of grouped informationcomprising the following 7 items and 13 types of information: (1)temperature; (2) humidity; (3) oscillation; (7) colored area ratio×fourcolors; (8) development toner amount×four colors; (9) slanting of paperfront end position; and (10) paper discharge timing. Hereafter, thisgrouped information will be referred to as first grouped information.

An abnormality relating to deterioration of the photosensitive body canbe determined on the basis of grouped information comprising thefollowing 7 items and 22 types of information: (1) temperature; (2)humidity; (5) uniform charging potential of the photosensitive body×fourcolors; (6) potential of the photosensitive body after exposure×fourcolors; (7) colored area ratio×four colors; (11) total current ofphotosensitive body×four colors; and (12) drive power of photosensitivebody×four colors. Hereafter, this grouped information will be referredto as second grouped information.

An abnormality relating to variation in the image density can bedetermined on the basis of grouped information comprising the following7 items and 22 types of information: (1) temperature; (2) humidity; (4)toner concentration×four colors; (5) uniform charging potential of thephotosensitive body×four colors; (6) potential of the photosensitivebody after exposure×four colors; (7) colored area ratio×four colors; and(8) development toner amount×four colors. Hereafter, this groupedinformation will be referred to as third grouped information.

As is clear from FIG. 19, the first, second, and third groupedinformation each have a different combination of information. This isdue to the fact that the combination of information required todetermine the individual abnormalities in each category differsaccording to the category. Hence, by obtaining at least two or more setsof grouped information differing in their combinations of informationand determining the respective Mahalanobis distances D thereof,specification of the type of the abnormality that is occurring can benarrowed to a category unit. In the example in FIG. 19, by determiningthe Mahalanobis distance D for each of the first, second, and third setsof grouped information, the abnormality type can be narrowed to thecorresponding one of the three categories.

To determine the Mahalanobis distance D, an inverse matrix A having thesame combination as the grouped information obtained periodically fromthe detection subject copier must be constructed. In FIG. 19, forexample, if an inverse matrix A comprising the 12 items and 33 types (5items+7 items×four colors) of information is used in common for all ofthe first, second, and third group information, abnormalities cannot bedetermined accurately. In the case of the first grouped information, theMahalanobis distance D must be determined using an inverse matrix Acomprising the same 7 items and 13 types of information that areincluded therein. Accordingly, inverse matrices A for determining theMahalanobis distance D in each category must be prepared prior todetermination.

There are two main methods of preparing an inverse matrix A for therespective sets of grouped information. In the first method, uniqueinverse matrices A (or alternative normal group data sets) for each setof grouped information are stored in the information storage means suchas the ROM 1 c. In the second method, an inverse matrix A is stored onlyfor an all-type set of grouped information comprising at least all ofthe types of information included in each set of grouped information.When this method is used, the individual inverse matrices A for therespective sets of grouped information are constructed respectively onthe basis of a desired combination of normal values selected from theinverse matrix A constituted by the collection of all-type groupedinformation. In FIG. 19, for example, only the inverse matrix Aconstituted by the collection of all-type grouped information (12 items,33 types) is stored. The inverse matrix A constituted by the collectionof first grouped information corresponding to a paper jam is thenconstructed by selecting 7 items and 13 types of information from theall-type grouped information. With this method, the amount ofinformation to be stored in the information storage unit can be reducedbelow that of the first method. Hence in this copier, unique inversematrices A for each set of grouped information are constructed accordingto the second method.

When an inverse matrix A for each category is constructed frominformation selected from the all-type grouped information in thismanner, a Mahalanobis distance D can be determined for the all-typegrouped information as well as for each set of grouped information. Bydetermining the former Mahalanobis distance D, abnormalities in othercategories can be determined as well as abnormalities in the categoriescorresponding respectively to the sets of grouped information. Forexample, by determining the Mahalanobis distance D of the all-typegrouped information in the example in FIG. 19, an abnormality can bedetermined in another category in addition to the paper jam,photosensitive body deterioration, and image density variationcategories.

FIG. 20 shows an example of a relationship between each category and theMahalanobis distance. Note that in FIG. 20, (D₀)² indicates the squarevalue of the Mahalanobis distance of the all-type grouped information(12 items, 33 types) in FIG. 19. Further, (D₁)² indicates the squarevalue of the Mahalanobis distance of the first grouped information (7items, 13 types) corresponding to an abnormality relating to a paperjam. (D₂)² indicates the square value of the Mahalanobis distance of thesecond grouped information (7 items, 22 types) corresponding to anabnormality relating to deterioration of the photosensitive body. (D₃)²indicates the square value of the Mahalanobis distance of the thirdgrouped information (7 items, 22 types) corresponding to an abnormalityrelating to variation in the image density.

As shown in FIG. 20, although the Mahalanobis distances (D₁)², (D₂)²,(D₃)² corresponding to each category are all lower than the threshold10, this does not necessarily mean that there are absolutely noabnormalities in the copier. Even though these Mahalanobis distances areless than the threshold, the Mahalanobis distance (D₀)² of the all-typegrouped information may be equal to or greater than the threshold. Insuch a case, it may be considered that an abnormality has occurred in acategory which does not correspond to any of the paper jam,photosensitive body deterioration, and image density variationcategories. Conversely, even when one of the Mahalanobis distances(D₁)², (D₂)², (D₃)² falls below the threshold 10, this does notnecessarily mean that the Mahalanobis distance (D₀)² of the all-typegrouped information also equals or exceeds the threshold. Even thoughthe copier as a whole may not be in an abnormal state, a minorabnormality may be discovered by focussing on each category one by one.In such a case, one of the Mahalanobis distances for the threecategories equals or exceeds the threshold, whereas the Mahalanobisdistance (D₀)² of the all-type grouped information falls below thethreshold.

By determining the Mahalanobis distance (D₀)² of the all-type groupedinformation in addition to the Mahalanobis distances (D₁)², (D₂)², (D₃)²for each category in this manner, it is also possible to determine theextent of the abnormality (whether or not the abnormality is minor) ineach category. Hence in this copier, abnormalities are determined on thebasis of the plurality of Mahalanobis distances correspondingindividually to the respective sets of grouped information, and theMahalanobis distance (D₀)² of the all-type grouped information.

Note that an example was described in which the thresholds for therespective Mahalanobis distances were all set to 10, but it ispreferable that the thresholds be set to different values in accordancewith the actual abnormalities.

There are two main methods of storing the inverse matrix A or thealternative normal group data set (the obtained data table, for example)in the information storage means such as the ROM 1 c. In the firstmethod, a normal standard device is operated to obtain a standardinverse matrix A, and the same inverse matrix A is stored in advance,prior to factory shipment, in the information storage means of eachindividual finished copier. In the second method, the individualfinished copiers are shipped without storing the inverse matrix A, andthe inverse matrix A is stored on the basis of the obtained results ofvarious information obtained during an initial operation at the shipmentdestination. Immediately after shipment, the finished copiers are in anormal state, having recently undergone inspection, and therefore theobtained results of the various information obtained during the initialoperation may be used as normal values. When the second method isemployed, an inverse matrix constructed on the basis of variousinformation obtained in reality in the individual finished copiers,rather than an inverse matrix constructed on the basis of a testoperation of a standard machine, is used as the inverse matrix A (or thealternative normal group data set). Hence, variation among finishedproducts in the normal values of the various information used todetermine an abnormality, caused by precision errors in the variouscomponents and so on, can be avoided, thus preventing deterioration ofthe determination precision. Moreover, the inverse matrix A isconstructed automatically at the shipment destination, and hence costincreases arising when the inverse matrix A is constructed at thefactory before shipment by performing a test operation on each finishedproduct can also be avoided. Therefore, in this copier the inversematrix A (or the alternative normal group data set) is constructedaccording to the second method during an initial operation at theshipment destination.

When the copier determines that an abnormality has occurred on the basisof a comparison between the calculated Mahalanobis distance D and thethreshold, fault warning information is displayed on the operationdisplay unit 3 as described above to notify the user or the like of theabnormality. Hence the operation display unit 3 is caused to function asnotification means for notifying the determination results of theabnormality determining apparatus. The notification means may performnotification through sound or notification through recording on arecording medium instead of notification through display.

The fault warning information may take any form, such as information,characters, words, numerical values such as the Mahalanobis distance D,a graph, and so on, providing the user or the like is informed of thedanger of a fault occurring. Further, in addition to, or instead of,informing a person at the shipment destination, a person in a remotemonitoring center may be informed via a communication line, as shown inFIG. 14. In so doing, the diagnosis of a specialist can be obtained. Theabnormality determination results are preferably stored in succession inthe information storage means such as the RAM 1 b. By storing thedetermination results in succession, the temporal progression of theabnormality and so on can be investigated at a later stage.

Depending on the determination result, it is desirable that the imageforming conditions be modified or a part of the image forming operationbe restricted. More specifically, the following responses in (a) to (c)may be considered.

(a) Halting the Apparatus

In cases such as when the Mahalanobis distance D reaches the abnormalitythreshold or the increase rate of the Mahalanobis distance D rises overtime, the apparatus may be halted forcibly and a request for maintenancetransmitted to the user.

(b) Restricting the Image Forming Operation or Modifying the ControlParameters

-   (b-1) Modifying the color mode-   (b-2) Modifying the recording speed-   (b-3) Modifying the screen ruling in the halftone portion of the    image-   (b-4) Modifying the halftone processing method-   (b-5) Restricting the types of paper that can be used-   (b-6) Modifying the registration control parameters-   (b-7) Modifying the image formation process parameters (uniform    charging potential, exposure amount, development bias, transfer    bias, etc.).    (c) Replenishing or Replacing Consumables or Components

Replenishment or replacement may be performed automatically on the basisof the Mahalanobis distance D calculation result.

Depending on the type of the abnormality that has occurred, theabnormality may be repaired automatically using a type of mechanism orfunction. By implementing control to repair such types of abnormalityautomatically, maintainability can be improved even further.

Up to this point, examples in which the abnormality determiningapparatus is installed in the main body of the copier have beendescribed. However, as shown in FIG. 15, the abnormality determiningapparatus may be constituted separately to the copier. In this case,reception means of the abnormality determining apparatus for receivingvarious information transmitted from the copier over a communicationline function as the information obtaining means of the abnormalitydetermining apparatus, rather than the various sensors and control unitinstalled in the copier. As a result, determination and diagnosis of anabnormality can be performed in a remote location removed from thecopier. Moreover, as shown in FIG. 16, abnormalities in each of aplurality of copiers can be determined by having a single abnormalitydetermining apparatus manage the plurality of copiers centrally.Further, if transmission means for transmitting a determination resultto the outside over a communication line are provided in the abnormalitydetermining apparatus, the determination result can be transmitted tovarious copiers disposed indifferent remote locations, and thus notifiedto the respective operators. The communication line may take any form,either wired or wireless, using optical fiber instead of electric lines,and so on.

In this copier, as described above, a normal group data set (the inversematrix A, for example) for the set of all-type grouped informationconstituted by at least all of the types of information included in thevarious sets of grouped information is stored as a normal group data setin the information storage means such as the ROM. The CPU 1 a serving asdetermination means then constructs unique normal group data sets foreach set of grouped information on the basis of a combination of normalvalues selected from the normal group data set for the all-type groupedinformation. With this constitution, for the reasons described above,the amount of information to be stored in the information storage meanscan be reduced in comparison with a case where unique normal group datasets are stored respectively for each set of grouped information.

Further, in this copier the CPU 1 a determines the presence of anabnormality in the detection subject copier on the basis of a pluralityof Mahalanobis distances corresponding individually to the various setsof grouped information, constituted by combinations of several pieces ofinformation from the all-type grouped information, and the Mahalanobisdistance of the all-type grouped information. With this constitution,for the reasons described above, abnormalities can be determined inother categories in addition to abnormalities in the categoriescorresponding to the various sets of grouped information, such asabnormalities relating to a paper jam, abnormalities relating to adeterioration of the photosensitive body, and abnormalities relating tovariation in the image density. Moreover, the extent of the abnormalityin each category (whether or not the abnormality is minor) can bedetermined.

Further, in this copier, the printer unit 100 and paper feed unit 200serving as image forming means develop a latent image formed on aphotosensitive body serving as a latent image carrier into a toner imageusing a developing unit serving as developing means, and then transferthe toner image onto transfer paper serving as a recording medium usingtransfer means. With this constitution, abnormalities in theelectrophotographic image forming process can be detected by theabnormality determining apparatus. Electrophotographic image formingapparatuses feature (1) a large number of constitutional components anda complicated development causal relationship, (2) a tendency to beaffected by the usage environment, for example the temperature andhumidity, (3) a tendency to be affected by deterioration of consumablessuch as units and components, (4) large differences in usage conditionsdepending on the user, and so on. In an image forming apparatus havingsuch a complicated constitution and development process, evenabnormalities such as faults having no obvious cause can be predicted bymeans of simple data processing.

Further, in this copier, at least one of the plurality of types ofinformation obtained by the information obtaining means is detectioninformation detected by sensors, control parameter information used tocontrol the image forming apparatus, image information for forming alatent image, and information relating to a toner image followingdevelopment. The detection value information detected by sensorsprovided in the copier includes information relating to the internalstate of the apparatus and the peripheral state of the apparatus, whichare closely linked to the state of the copier. The control parametervalue information, which is used to control the copier, includesinformation regarding the content of the control, which greatly affectsthe operational state of the copier. The image information for forming alatent image and information relating to a toner image followingdevelopment include information regarding the image forming function,which greatly affects the state of the copier. By calculating theMahalanobis distance D from this information, changes of state in thecopier can be determined with a high degree of precision, and hence theoccurrence of an abnormality can also be predicted with a high degree ofprecision.

Further, in this copier, the CPU 1 a is caused to function as normalgroup data set construction means for constructing a normal group dataset such as the inverse matrix A on the basis of the obtained results ofthe information obtaining means. With this constitution, for the reasonsdescribed above, deterioration of the determination precision caused bycomponent errors in each finished printer can be avoided, and costincreases arising when a test operation is performed to construct eachinverse matrix for each finished product prior to shipment can also beavoided.

Further, in this copier, notification means such as the operationdisplay unit 3 are provided for issuing fault warning information, whichis the determination result of the abnormality determining apparatus.With this constitution, a user can be informed that a fault may occur,and is thus provided with a sufficient preparation period for carryingout appropriate fault-prevention measures.

Further, by providing transmission means in this copier for transmittingthe determination result of the abnormality determining apparatus to theoutside over a communication line, for the reasons described above, thediagnosis of a specialist in a remote location can be obtained.

Further, by providing operation restricting means in this copier forplacing restrictions on the image forming operation on the basis of thedetermination result of the abnormality determining apparatus, temporaryrestrictions can be placed on specific operations in accordance with theresult of an abnormality prediction, and thus heavy damage can beforestalled.

Further, by providing restoration control means in this copier forperforming restoration control to restore the functions of the imageforming means on the basis of the determination result of theabnormality determining apparatus, a restoration control mode can beexecuted in accordance with the result of an abnormality prediction, andthus heavy damage can be forestalled.

Further, in the example where the abnormality determining apparatus isconstituted separately to the copier, reception means for receiving aplurality of information transmitted from an external copier via acommunication line are provided as the information obtaining means. Withthis constitution, the plurality of information is received and obtainedfrom a copier disposed in a remote location, and hence an abnormality inthe copier can be determined without being on site.

Also in this example, transmission means are provided for transmittingthe determination result of the determining means to the externalcopier. With this constitution, the determination result is transmittedby the transmission means, and hence a user in the remote location inwhich the copier is disposed can be informed of the occurrence of anabnormality.

Also in this example, information relating to the copier serving as animage forming apparatus is obtained as the plurality of information,whereupon the presence of abnormalities in the information isdetermined. With this constitution, abnormalities can be determined inan externally disposed copier serving as a detection subject.

According to the first embodiment as described above, a Mahalanobisdistance is determined on the basis of a normal group data set stored ininformation storage means such as a hard disk, RAM, or ROM and groupedinformation comprising a plurality of information obtained from adetection subject, and this Mahalanobis distance is used to determinethe presence of an abnormality. As a result, increasingly complicatedcontrol occurring when a plurality of abnormalities are detectedindividually according to the presence of their respective causes can beavoided.

Also according to the first embodiment, Mahalanobis distances aredetermined for at least two or more sets of grouped information, forexample grouped information comprising a plurality of informationrelating to the paper feed system in the image forming apparatus,grouped information comprising a plurality of information relating tothe image writing system, and soon. By evaluating the respectiveMahalanobis distances, occurring abnormalities can be specified to acertain extent according to category, for example a category relating tothe paper feed system, a category relating to the image writing system,and so on.

Second Embodiment

The second embodiment mainly serves to achieve the aforementioned secondobject of the present invention.

Note that FIGS. 1 to 13 and 17 to 19 and the description pertaining tothese drawings, which were referenced in the first embodiment, are alsoapplied substantially to the second embodiment. Accordingly, repetitivedescription has been omitted, and the particular features of the secondembodiment are described in detail.

First, the basic constitution of an abnormality determining apparatusaccording to the second embodiment will be described.

It is assumed that the detection subject of this abnormality determiningapparatus is the same copier as that described up to this point, andthat the abnormality determining apparatus determines the presence of anabnormality in the interior of the copier.

The constitution of the main parts of an electric circuit in thisabnormality determining apparatus is shown in FIG. 21. As shown in thedrawing, the abnormality determining apparatus comprises an informationobtaining unit 501 serving as information obtaining means for obtaininginformation about an object, an abnormality determining unit 502 servingas abnormality determining means, an information storage unit serving asinformation storage means, a data input unit 504 serving as data inputmeans, and so on. A determination result output unit 505 serving asdetermination result outputting means for outputting the result of adetermination performed by the abnormality determining means is alsoprovided.

The information obtaining unit 501 obtains the aforementionedinformation of (1) to (12) from the detection subject copier, not shownin the drawing. The information of (1) to (12) obtained by theinformation obtaining unit 501 is transmitted to the abnormalitydetermining unit 502. The abnormality determining unit 502 comprisescalculation means (a CPU 501 a in the illustrated example) forperforming various calculations required to determine the presence of anabnormality. Hence the information transmitted from the informationobtaining unit 501 is used as is in the calculation processing fordetermining an abnormality, or used after being stored in theinformation storage unit 503. More specifically, predeterminedcalculations are implemented on the basis of the information of (1) to(12) transmitted from the information obtaining unit 501, and thepresence of an abnormality in the copier is determined on the basis ofthe result of a comparison between the calculation result and apredetermined threshold stored in the information storage unit 503.

The result of the determination performed by the abnormality determiningunit 502 is output by the determination result output unit 505. Thisoutput may take the form of characters to be recognized by a user of thecopier, an image display, audio output, and so on, and also includes amode in which the determination result information is output to anexternal device such as a personal computer or printer. By means of thisoutput, the determination result of the abnormality determining unit 502is acknowledged by the user of the copier, a serviceperson in a remotelocation, and so on. Note that the information obtaining unit 501 isconstituted by RAM, ROM, a hard disk, or similar, which storesinformation such as a control programs and algorithm, for example, aswell as the various information obtained by the information obtainingunit 501. The data input unit 504 receives data input for storing athreshold to be described below in the information storage unit 503, andthe threshold data that are received in this manner are transmitted tothe information storage unit 503 via the abnormality determining unit502.

Next, the characteristic constitution of this abnormality determiningapparatus will be described.

The abnormality determining unit 502 is constituted to determine ageneral abnormality comprising a plurality of types of abnormality, anda plurality of individual abnormalities constituting this plurality oftypes of abnormality, as an abnormality in the copier. Morespecifically, three abnormalities relating to a paper jam, deteriorationof the photosensitive bodies, and variation in the image density aredetermined respectively as the plurality of individual abnormalities.The general abnormality includes these three individual abnormalities.

When determining the three individual abnormalities, the aforementionedthresholds corresponding to each individual abnormality are read fromthe information storage unit 503 and compared with the aforementionedcalculation result. These thresholds are stored in the informationstorage unit 503 by means of data input into the data input unit 504serving as data input means.

In the abnormality determining apparatus constituted in this manner, thepresence of the individual abnormalities is determined only when thegeneral abnormality including the three individual abnormalities isdetected, and hence complicated control required to confirm the presenceor absence of each individual abnormality upon each determination can beavoided. Moreover, when the general abnormality is detected, thedetected individual abnormality is specified from among the threeindividual abnormalities included in the general abnormality. By meansof this specification, the maintenance response following detection ofthe general abnormality can be prevented from becoming too complicated.

Also in the abnormality determining apparatus, the three thresholds usedrespectively to determine the three individual abnormalities are setinitially by a serviceperson or user and updated by the user through aninput operation into the data input means. By means of this initialsetting and updating, the individual abnormalities can be determinedwith a degree of precision suited to each individual user.

This abnormality determining apparatus may be constituted integrallywith the copier serving as the detection subject to function as apart ofthe copier, or may be constituted separately to the copier to determinethe presence of an abnormality on the basis of the information of (1) to(12) transmitted from the copier.

In the latter case, i.e. when the abnormality determining apparatus isconstituted separately to the copier, a plurality of copiers 600 can bemanaged together by a single abnormality determining apparatus 500 in aremote location, as shown in FIG. 22. Further, as shown in FIG. 23, theplurality of copiers 600 connected to a plurality of personal computersPC on a network such as an in-house LAN or the Internet can be managedtogether by the single abnormality determining apparatus 500 via acommunication line. When performing general management of this type, ifthe data input portion 504 is constituted to receive data input of thethresholds transmitted over the communication line, then data input ofthe thresholds into the abnormality determining apparatus can beperformed by a user in a remote location. Further, if the determinationresult output unit 505 is constituted to output the determination resultover the communication line, then the determination result can betransmitted to various copiers disposed in different remote locations,and thus notifies to the respective users. The communication line maytake any form, either wired or wireless, using optical fiber instead ofelectric lines, and so on. Note that when the abnormality determiningapparatus is constituted separately to the copier, the informationobtaining means comprising the control unit, various sensors, operationdisplay unit (1, 2, 3 in FIG. 4), and so on in the copier do notfunction as the information obtaining unit 501 of the abnormalitydetermining apparatus. Instead, reception means for receiving variousinformation transmitted from the copier over the wired or wirelesscommunication line function as the information obtaining unit 501 of theabnormality determining apparatus.

In the former case, on the other hand, that is when the abnormalitydetermining apparatus 500 is constituted integrally with the copier 600to function as a part of the copier 600, as shown in FIG. 24, theinformation obtaining means of the copier 600 also function as theinformation obtaining means of the abnormality determining apparatus500. More specifically, the information obtaining means comprising thecontrol unit 1, various sensors 2, operation display unit 3, and so on,shown in FIG. 4, function as the information obtaining unit 501 of theabnormality determining apparatus. In this case, the control unit 1 ofthe copier may double as the abnormality determining unit (502 in FIG.21) and the information storage unit (503 in FIG. 21) of the abnormalitydetermining apparatus. Furthermore, the operation display unit 3 of thecopier may double as the data input unit (504 in FIG. 21) anddetermination result output unit (505 in FIG. 21) of the abnormalitydetermining apparatus. If the determination result output unit isconstituted to output determination results via a communication line, aremote repair service organization can be notified of an abnormality inthe copier automatically.

As described above, the abnormality determining apparatus may beconstituted integrally with or separately to the copier. In thefollowing, however, an example in which the abnormality determiningapparatus is constituted integrally with the copier will be described.

The abnormality determining apparatus determines the presence of thegeneral abnormality and individual abnormalities described above bydetermining a Mahalanobis distance using an MTS method on the basis ofgrouped information comprising the plurality of types of information (1)to (12) obtained by the information obtaining unit 501. To realize thisdetermination, a normal group data set obtained in advance is stored inthe information storage unit 503. The abnormality determining unit 502determines the Mahalanobis distance on the basis of the normal groupdata set and the grouped information comprising all or some combinationsof the information of (1) to (12).

To determine the Mahalanobis distance, the normal group data set and theinverse matrix thereof must be constructed before determining thepresence of an abnormality. As described above, FIG. 17 shows anobtained data table used in a normal data obtaining process performed toconstruct the normal group data set on the basis of the information of(1) to (12) obtained from the copier in a normal state. In this obtaineddata table, an example is illustrated in which n sets of groupedinformation comprising k types of information are obtained.

Note that the process of obtaining the information of (1) to (12) thatis performed in this normal data obtaining process is not an informationobtaining process performed in order to determine an abnormality, butsimply a process performed to construct the normal group data set. Theinformation obtaining process performed to determine an abnormality isimplemented when the normal group data set has been constructed as aresult of this normal data obtaining process.

The normal data obtaining process is performed by obtaining from thecopier, which is operated in a normal state, a plurality of combinationsof the information of (1) to (12) as normal grouped information. Astandard device for obtaining a single normal group data set common to aplurality of finished copiers to be shipped from the factory may be usedas the copier from which the data are obtained, or each of the finishedcopiers may be operated individually to obtain unique normal group datasets.

In the normal data obtaining process, first, k types of information y₁₁,y₁₂, . . . , y_(1k), constituting a first set of grouped information,are obtained respectively by the information obtaining means of thecopier, and stored in the obtained data table of FIG. 17 as data on thefirst row of the table. Next, k types of information y₂₁, y₂₂, . . . ,y_(2k), constituting a second set of grouped information, are obtainedrespectively by the information obtaining means, and stored in theobtained data table as data on the second row of the table. The thirdset to the nth set of grouped information are then obtained similarlyand stored in the obtained data table as data on the third row to thenth row of the table. Finally, the average and standard deviation σ ofthe respective n sets are determined for the k types of informationconstituting each set of grouped information, and stored in the obtaineddata table as data on the n+1 and n+2 rows. Thus the data in theconstructed obtained data table are used as the normal group data set.

Once the normal data obtaining process is complete, an informationnormalization process is implemented to construct a normalized datatable. As described above, FIG. 18 shows a normalized data tableconstructed in this information normalization process. This normalizeddata table is constructed on the basis of the obtained data table shownin FIG. 17.

Hereafter, the description of the first embodiment pertaining to Eqs.(1) to (4) applies similarly to the second embodiment, and thereforerepetitive description thereof has been omitted.

The inverse matrix A is constructed by this series of processescomprising the normal data obtaining process, information normalizationprocess, correlation coefficient calculation process, and matrixtransformation process. All or a part of these processes may beimplemented by the abnormality determining apparatus. When all of theprocesses are implemented, there is no need to pre-store the normalgroup data set in the information storage means of the copier duringfactory shipment. Instead, the information of (1) to (12) can beobtained as normal grouped information during an initial operatingperiod at the shipment destination, in which an abnormality is highlyunlikely to occur, and the normal group data set or inverse matrix A canbe constructed from this information. Immediately after shipment, thefinished copiers are in a normal state, having recently undergoneinspection, and therefore the obtained results of the variousinformation obtained during the initial operation may be used as normalvalues. When any one of the series of processes described above is notimplemented by the abnormality determining apparatus, the inverse matrixA must be stored in the information storage means of the copier duringfactory shipment. In this case, the pre-stored inverse matrix A may beconstituted by an inverse matrix common to each finished copier, whichis constructed on the basis of a normal group data set obtained from theaforementioned standard device, or individual inverse matrices may beconstructed by obtaining individual normal group data sets from eachfinished copier. Note that the normal group data set may be pre-stored,whereby the abnormality determining apparatus implements transformationof the inverse matrix A from the normal group data set.

As noted above, a common normal group data set for each finished copier,which is obtained from a standard device, may be used as the normalgroup data set, or each finished copier may be operated individually toobtain a unique normal group dataset. In the latter case, variationamong finished products in the normal values of the various informationused to determine an abnormality, caused by precision errors in thevarious components and so on, can be avoided, thus preventingdeterioration of the determination precision. Moreover, by constitutingthe abnormality determining apparatus so as to obtain the normal groupdata set during the initial operating period after factory shipment,cost increases due to the labor required to test run the finishedproducts at the factory prior to shipment in order to obtain therespective normal group data sets can be avoided.

Regardless of the manner in which the normal group data set is obtained,the inverse matrix A constructed as described above is stored in theinformation storage unit 503 of the abnormality determining apparatusduring abnormality determination. The abnormality determining unit 502then calculates the Mahalanobis distance D on the basis of the set ofall-type grouped information, comprising all of the information of (1)to (12) obtained by the information obtaining unit 501, the inversematrix A, and the aforementioned Eq. (5).

As shown in FIG. 13, in the procedure for calculating the Mahalanobisdistance D in this embodiment, first k types of data x₁, x₂, . . . ,x_(k) in any condition are obtained (S2-1). The data types correspond toy₁₁, y₁₂, . . . , y_(1k), and so on. Next, the obtained data arenormalized respectively to X₁, X₂, . . . , X_(k) on the basis of theaforementioned Eq. (1). Then, using the aforementioned Eq. (5), which isdetermined using the element a_(kk) of the constructed inverse matrix A,the square of the Mahalanobis distance D is calculated.

Note that in the copier, the information of (1) to (12) is obtained, butsince the information in (4) to (8), (11), and (12) is obtained for thefour colors (four types), the k in x_(k) equals 5+7×4=33 [types].

The abnormality determining unit 502 determines the presence of thegeneral abnormality by comparing the Mahalanobis distance D for theall-type grouped information (grouped information constituted by 33types of information) determined in this manner with the generalabnormality threshold. As the Mahalanobis distance D increases beyond[1], the detected data diverge further from a normal state. When theMahalanobis distance D exceeds the general abnormality threshold, it isdetermined that the general abnormality is “present”.

When it is determined that the general abnormality is present, theabnormality determining apparatus determines the presence of the threeindividual abnormalities (paper jam, photosensitive body deterioration,image density variation) included in the general abnormality,respectively. FIG. 19, which was referenced above, shows an example of arelationship between the various individual abnormalities in the copierand the grouped information required to determine their presence.

The first through third sets of grouped information relating to each ofthe three abnormality types have been described already with referenceto FIG. 19. As is clear from FIG. 19, the first, second, and third setsof group information each have a different combination of information.This is due to the fact that the combination of information required todetermine an abnormality differs according to the type of abnormality.By determining the Mahalanobis distance D for each of the first, second,and third grouped information in the example in FIG. 19, the type ofabnormality can be narrowed down.

Hence when the abnormality determining apparatus determines the generalabnormality to be “present”, the Mahalanobis distance D of each of thefirst, second, and third grouped information is determined. By comparingthe respective determined Mahalanobis distances D with the thresholds,the presence of an abnormality relating to a paper jam, deterioration ofthe photosensitive body, and variation in the image density isdetermined. Note that the values of the thresholds for determining theindividual abnormalities relating to a paper jam, deterioration of thephotosensitive body, and variation in the image density typically differfrom the value of the general abnormality threshold. Accordingly, thethree Mahalanobis distances D determined on the basis of the first,second, and third grouped information respectively are compared toindividually corresponding thresholds relating to a paper jam,deterioration of the photosensitive body, and variation in the imagedensity.

In this abnormality determining apparatus, a serviceperson or userinputs the three thresholds relating to a paper jam, deterioration ofthe photosensitive body, and image density variation into the data inputunit 504 in accordance with the user information, and hence theserviceperson or user is capable of performing initial setting andupdating of these thresholds. Examples of the user information reflectedin the three thresholds include the copier maintenance proficiency anddegree of fault perception. The reason for reflecting this informationin the thresholds is as described above. Other examples of userinformation that may be reflected in the thresholds include the intendeduse of the copier, the industry sector, the department, the relationshipbetween paper size and usage frequency, and the relationship between thetype of output image and output frequency. Naturally, the required imagequality, and therefore the user's degree of fault perception, differwhen the intended use of the copier is to produce a written product suchas an instruction manual, and when the intended use is to create apersonal printout, test-print an image, and so on. The required imagequality and the frequency of abnormality occurrence also differaccording to the industry sector or department of the user. It is alsopossible for a fault to be perceived or not perceived depending on thepaper size, regardless of personal differences. For example, when thevicinity of the end part of a drum-form photosensitive body is damaged,the resulting image disturbance occurs near the end portion ofcomparatively large paper, but does not occur on comparatively smallpaper. Hence, this type of image disturbance is more likely to beperceived by a user who uses comparatively large paper frequently,regardless of personal differences. Further, deterioration of the imagequality is more likely to be perceived on a photographic image than atext image, regardless of personal differences, and hence image qualitydeterioration is more likely to be perceived by a user who outputsphotographic images frequently. By reflecting the intended use of thecopier, the industry sector, the department, the relationship betweenpaper size and usage frequency, and the relationship between the type ofoutput image and the output frequency in the three thresholds, theindividual abnormalities can be detected with a precision correspondingto each individual user.

An example of a method for reflecting user information in the thresholdsis multiplication of a coefficient corresponding to the user informationby a standard threshold. This standard threshold is determined on thebasis of a typical user (a user with a typical level of proficiency andso on). FIG. 25 shows an example of a standard threshold for the threethresholds relating to a paper jam, deterioration of the photosensitivebody, and variation in the image density.

The standard threshold shown in FIG. 25 is merely one example thereof,and the value that is actually set is not limited thereto. Moreover, anexample is shown in which the standard threshold increases in successionof deterioration of the photosensitive body, paper jam, and variation inthe image density, but the actual succession is not limited thereto.

Next, FIG. 26 shows an example of the relationship between theproficiency level, serving as user information, and the thresholdcoefficient.

In FIG. 26, as the proficiency level rises from low, to medium, to high,the threshold coefficient increases from “0.9”, to “1.0”, to “1.2”. Thereason for this is as follows. As the value of the Mahalanobis distanceD increases, so does the extent of the abnormality. Accordingly, as thethreshold that is compared to the Mahalanobis distance D decreases, theabnormality is detected more acutely. Meanwhile, as the proficiencylevel of the user rises, even when the extent of the abnormality staysthe same, it is more unlikely that a request for repairs will be issued.Therefore, to match the abnormality detection precision to eachindividual user, the thresholds must be increased so that an abnormalityis less likely to be detected as the proficiency level of the userrises. Hence the threshold coefficient to be multiplied by the thresholdrises from “0.9”, to “1.0”, to “1.2” as the proficiency level increasesfrom low, to medium, to high.

Next, FIG. 27 shows an example of the relationship between the degree offault perception, serving as user information, and the thresholdcoefficient.

In FIG. 27, the threshold coefficient decreases from “1.2”, to “1.0”, to“0.8” as the degree of fault perception increases from low, to medium,to high. The reason for this is as follows. As noted above, anabnormality is detected more acutely as the threshold to be compared tothe Mahalanobis distance D decreases. Meanwhile, as the user's degree offault perception rises, even when the extent of the abnormality staysthe same, it is more likely that a request for repairs will be issued.Therefore, to match the abnormality detection precision to eachindividual user, the thresholds must be decreased so that an abnormalityis more likely to be detected as the user's degree of fault perceptionrises. Hence the threshold coefficient to be multiplied by the thresholddecreases from “1.2”, to “1.0”, to “0.8” as the degree of faultperception rises from low, to medium, to high.

Next, FIG. 28 shows an example of the relationship between the industrysector and department of the user, and the threshold coefficient.

When the industry sector of the user is printing-related and thedepartment of the user is production-related, it is highly likely thatthe intended use of the copier will be to produce written materials. Itis therefore highly likely that the user will have an acute perceptionof decreases in image quality and increases in the frequency of paperjams. Hence in FIG. 28, the threshold coefficient is set to a minimumvalue of “0.8” in this case.

FIG. 29 shows a relationship between the type of output image, theoutput frequency, and the threshold coefficient.

An abnormality in the image quality (variation in the image density, forexample) typically becomes more likely to be perceived in order ofwritten documents, drawings, advertising leaflets, and photographs,regardless of personal differences among users in the degree ofperception. Hence a user who outputs written documents more often thanother types of images is less likely to perceive an abnormality in theimage quality, regardless of personal differences. In contrast, a userwho outputs photographs more often than other types of images is morelikely to perceive an abnormality in the image quality. Therefore, inthe example in FIG. 29, the threshold coefficients are set inconsideration of the output frequency order of the four types of imagescomprising written documents, drawings, advertising leaflets, andphotographs, and the order in which abnormalities are perceived in thesefour types of images. For example, an abnormality in the image qualityis least likely to be perceived, regardless of personal differences,when written documents, drawings, advertising leaflets, and photographsare printed with a decreasing order of output frequency. In this case,the threshold coefficient takes a value of “1.00”, which is lower thanall of the other output frequency orders. Conversely, an abnormality inthe image quality is most likely to be perceived, regardless of personaldifferences, when photographs, advertising leaflets, drawings, andwritten documents are printed with a decreasing order of outputfrequency. In this case, the threshold coefficient takes a value of“1.50”, which is higher than all of the other output frequency orders.

As described above, by reflecting user information in the thresholds(relating to a paper jam, deterioration of the photosensitive body, andvariation in the image density), the individual abnormalities can bedetected with a precision corresponding to each individual user.

As well as user information, it is desirable that information regardingthe environment in which the copier is placed be reflected in thethresholds (relating to a paper jam, deterioration of the photosensitivebody, and variation in the image density). The reason for this is asfollows. Even when the calculation result of the Mahalanobis distance Dis constant, it is possible for the degree of perception of anabnormality to vary according to the environment, regardless of personaldifferences. For example, even when the calculation result of theMahalanobis distance D is constant, paper jams may occur more or lessfrequently depending on the humidity of the environment in which thecopier is used. In such a case, inappropriate notification of theoccurrence of an abnormality due to a varying degree of abnormalityperception depending on the environment, regardless of personaldifferences, can be prevented by setting the thresholds in accordancewith information relating to the environment of the copier.

When an old copier is replaced with a new one due to circumstances suchas the old copier reaching the end of its lifespan, the thresholds(relating to a paper jam, deterioration of the photosensitive body, andvariation in the image density) in the new copier are preferably setinitially to the same values as those of the thresholds used in the oldcopier. The reason for this is as follows. Initial setting of thethresholds rarely results in values which are perfectly suited to theuser at that time, and hence it is preferable that the thresholds begradually updated to appropriate values in accordance with repeatedabnormality detection, and the degree of abnormality perception and soonof the user. By updating the thresholds in this manner, when an oldcopier is replaced with a new one, the thresholds used in the old copierare updated to values which are more suited to the user than theinitially set values, and are therefore highly likely to approach therequirements of the user. If the old thresholds are not employed in thenew copier, and values which reflect user information in only a generalsense are employed instead, these values become far removed from therequirements of the user. This is why the thresholds are set initiallyto the same values as those used in the old copier. In so doing,deterioration of the abnormality detection precision caused by initialsetting of the thresholds in a new copier to values which reflect userinformation in only a general sense can be avoided.

Further, the thresholds (relating to a paper jam, deterioration of thephotosensitive body, and variation in the image density) are preferablyupdated in accordance with information regarding the repair requesthistory of the user based on the occurrence of abnormalities. Byupdating the thresholds in this manner, the thresholds can be modifiedgradually from their initial setting to values corresponding to therequirements of the user.

The normal group data set stored in the information storage unit 503 ispreferably updated according to the relationship between thedetermination result of the general abnormality and the result of aninspection of the copier. More specifically, when an abnormality isconfirmed in the copier during an inspection despite the generalabnormality having been determined as “absent”, this indicates thatnon-normal grouped information is included in the normal group data set.As a result, the normal space range in the Mahalanobis space becomeslarger than usual, making it impossible to detect abnormalities. In thiscase, the normal group data set is updated by deleting the non-normalgrouped information from the normal group data set. The normal groupdata set may then be updated by adding new normal grouped information toreplace the deleted grouped information. By deleting the non-normalgrouped information, mis-detections due to such grouped informationbeing included in the normal group data set can be avoided. Note thatnon-normal grouped information can be identified by extracting datahaving a large standard deviation from the normalized data tabledescribed above.

In this abnormality determining apparatus, the information obtainingunit 501 and abnormality determining unit 502 are constituted to varythe frequency with which the various information is obtained and thefrequency with which the presence of the general abnormality isdetermined according to the Mahalanobis distance D, which serves as thecalculation result of the general abnormality. More specifically, whenthe Mahalanobis distance D of the general abnormality nears the generalabnormality threshold to a certain extent, the various informationobtaining frequency and the determination frequency are increased. Thereason for this will now be described using FIGS. 30 to 32.

FIG. 30 is a graph showing an example of a relationship between theMahalanobis distance D of the general abnormality in this copier and theelapsed time (running time). In the graph, the abnormality detectionthreshold refers to the general abnormality threshold used to determinedthe presence of the general abnormality. The fault occurrence thresholdtakes the same value as the Mahalanobis distance D when an individualabnormality has progressed to the extent that a fault occurs in thecopier. When the Mahalanobis distance D increases to the faultoccurrence threshold, a fault occurs in the copier. Depending on thetypes of individual abnormality included in the general abnormality, theincrease rate of the Mahalanobis distance D begins to rise rapidly afterapproaching the fault occurrence threshold to a certain extent, as shownin the graph. In such a case, detection of the general abnormalitydetection is greatly delayed.

Specifically, FIG. 31 is a graph showing the relationship between theMahalanobis distance D when the presence of the general abnormality isdetermined at time intervals of 4 t, and the elapsed time, in the copierhaving the characteristics shown in FIG. 30. In the graph, a faultoccurs between a time 32 t and a time 36 t, but at the time 32 t theMahalanobis distance D has not yet reached the abnormality detectionthreshold, and hence the general abnormality is not detected. After thetime 32 t, the next general abnormality determination is performed atthe time 36 t, but during this period, the abnormality progressesrapidly so that the general abnormality occurs before the time 36 t.Hence, in the example shown in the drawing, the general abnormality isdetected after a fault has occurred, and thus the occurrence of thegeneral abnormality cannot be predicted.

FIG. 32 is a graph showing an example of the relationship between theMahalanobis distance D, in a case where the general abnormalitydetermination frequency is raised when the Mahalanobis distance D of thegeneral abnormality approaches the abnormality detection threshold to acertain extent, and the elapsed time. In the graph, a determinationfrequency modification threshold is used to determine whether or not tomodify the determination frequency of the general abnormality, and isset to a smaller value than the abnormality detection threshold. In theillustrated example, the Mahalanobis distance D becomes gradually largeras time passes, and from a time 24 t, the increase rate (increase amountper unit time) of the Mahalanobis distance D begins to increase.Slightly before a time 28 t, the Mahalanobis distance D reaches thedetermination frequency modification threshold. The abnormalitydetermining unit 502 recognizes this at the time 28 t, and raises thedetermination frequency of the general abnormality from 4 t intervals to1 t intervals. The Mahalanobis distance D then reaches the abnormalitydetection threshold at a time 32.5 t. At a time 33 t, which is onlyslightly later than 32.5 t, the presence of the general abnormality isdetected by the abnormality determining unit 502, and at a time 34 t, afault occurs. By raising the determination frequency at the time 28 t,the general abnormality is detected before a fault occurs. Therefore, byconstituting the abnormality determining unit 502 to modify thefrequency with which the general abnormality is determined in accordancewith the Mahalanobis distance D of the calculation result, situations inwhich it becomes impossible to predict the occurrence of the generalabnormality due to a rapid increase in the increase rate of theMahalanobis distance D can be avoided.

Depending on the determination result, it is desirable that the imageforming conditions be modified or a part of the image forming operationbe restricted. More specifically, the following responses in (a) to (c)may be considered.

(a) Halting the Apparatus

In cases such as when the Mahalanobis distance D reaches the abnormalitythreshold or the increase rate of the Mahalanobis distance D rises overtime, the apparatus may be halted forcibly and a request for maintenancetransmitted to the user.

(b) Restricting the Image Forming Operation or Modifying the ControlParameters

-   (b-1) Modifying the color mode-   (b-2) Modifying the recording speed-   (b-3) Modifying the screen ruling in the halftone portion of the    image-   (b-4) Modifying the halftone processing method-   (b-5) Restricting the types of paper that can be used-   (b-6) Modifying the registration control parameters-   (b-7) Modifying the image formation process parameters (uniform    charging potential, exposure amount, development bias, transfer    bias, etc.).    (c) Replenishing or Replacing Consumables or Components

Replenishment or replacement may be performed automatically on the basisof the Mahalanobis distance D calculation result.

Depending on the type of the individual abnormality, it may be possibleto continue operations until preparations for repairs are complete byrestricting the functions of the copier even when a fault occurs as theindividual abnormality progresses. For example, assuming that thevicinity of the end portion of the drum shaft of a drum-shapedphotosensitive body is greatly damaged for some reason, when printing isperformed on large paper which uses substantially the entire axialdirection range of the photosensitive body, a dramatic deterioration inimage quality, contamination, and so on occur near the end portion ofthe paper. However, when printing is performed on small paper which neednot use the damaged region of the photosensitive body, such imagequality deterioration and contamination do not occur. Hence byrestricting the functions of the copier such that the use of large paperis prohibited when the vicinity of the end portion of the drum shaft ofthe drum-shaped photosensitive body is greatly damaged, the copier canbe operated to implement printing until preparations for repairs arecomplete. For this purpose, the abnormality determining apparatus isprovided with function restricting means for restricting the functionsof the copier in accordance with the occurrence of the individualabnormalities. FIG. 33 is a pattern diagram showing an example of adisplay screen on the operation display unit of the copier that isdisplayed when function restriction is performed by the functionrestricting means. This is an example of a display screen displayed toindicate that image quality deterioration and contamination can beavoided by using paper that is smaller than A4 size.

Next, a modification of this abnormality determining apparatus will bedescribed.

FIG. 34 shows the constitution of the main parts of an electric circuitin the abnormality determining apparatus according to this modification.Comparing this diagram to FIG. 21, it can be seen that the constitutionof the electric circuit of this abnormality determining apparatus issubstantially identical to that of the abnormality determining apparatusaccording to the second embodiment described above, but differs incomprising a data display unit 506, and in that a threshold setting unit507 serving as threshold setting means is constituted by the abnormalitydetermining unit 502, information storage unit 503, data input unit 504,and data display unit 506.

Likewise in this abnormality determining apparatus, the informationobtaining unit 501 is used to obtain the aforementioned information of(1) to (12) from the detection subject copier. The abnormalitydetermining unit 502 determines the presence of the general abnormalityand the three individual abnormalities relating to a paper jam,deterioration of the photosensitive body, and variation in the imagedensity, which are included in the general abnormality, on the basis ofvarious data stored in the information storage means and the informationof (1) to (12) obtained by the information obtaining unit 501.Determinations as to the presence of the respective abnormalities areperformed similarly to the second embodiment, i.e. by comparing theMahalanobis distance D to the unique thresholds of the three individualabnormalities. The presence of the three individual abnormalities isdetermined only when the general abnormality is detected. The datadisplay unit 506 is constituted by a liquid crystal display or the like,and displays images on the basis of image signals transmitted from theabnormality determining unit 502.

The threshold setting unit 507 constituted by the abnormalitydetermining unit 502, information storage unit 503, data input unit 504,and data display unit 506 sets the general abnormality threshold and therespective thresholds relating to a paper jam, deterioration of thephotosensitive body, and variation in the image density, which arestored in the information storage unit 503. A specific method ofperforming this setting is as follows. A question implementation programfor asking the user predetermined questions in order to obtain userinformation is stored in the information storage unit 503. Theabnormality determining unit 502 displays various question informationon the data display unit 506 on the basis of this questionimplementation program. Examples of these questions include “If paperjams began to occur frequently, would you be capable of searching forthe cause?”, “Are you capable of replacing a photosensitive body byyourself?”, and so on. Once the user has inputted response data to eachof these questions into the data input unit 504, the abnormalitydetermining unit 502 stores the inputted response data in theinformation storage unit 503 as user information.

When the question implementation program is complete, a plurality ofuser information is stored in the information storage unit 503. Theabnormality determining unit 502 then performs initial setting of thethree thresholds relating to a paper jam, deterioration of thephotosensitive body, and variation in the image density on the basis ofthe user information and the various data stored in the informationstorage unit 503. The various data used at this time are the data shownin FIGS. 25 to 29, for example. As a result of this initial setting, theuser information is reflected in the three thresholds relating to apaper jam, deterioration of the photosensitive body, and variation inthe image density, and hence the determination precision of theindividual abnormalities is matched to the user.

The abnormality determining apparatus constituted in this manner differsgreatly from the abnormality determining apparatus according to thefirst embodiment in that the data input into the data input unit 504 areuser information rather than the thresholds themselves. Instead ofhaving the user input the thresholds, user information is input in theform of responses to questions. In most cases, the user is unaware ofthe abnormality determination method. If the user is forced to calculateand input the respective thresholds relating to a paper jam,deterioration of the photosensitive body, and variation in the imagedensity while referring to a manual or the like, s/he may feelinconvenienced. However, by inputting user information in the form ofresponses to questions and setting the thresholds on the basis of theseresponses, as in this abnormality determining apparatus, situations suchas that described above, in which the user feels inconvenienced, can beavoided. Moreover, situations in which the user is forced to performcomplicated calculations in order to determine the thresholds can beavoided.

The threshold setting unit 507 not only performs initial setting of thethresholds relating to a paper jam, deterioration of the photosensitivebody, and variation in the image density on the basis of the userinformation, but also alters these thresholds if necessary. Morespecifically, as noted above, the initially set thresholds are rarelyperfectly suited to the user. In most cases, the thresholds do notbecome complete unless they are adjusted little by little through realexperience. It is therefore desirable that the thresholds correspondingto the respective individual abnormalities be updated gradually inaccordance with the detection precision of each individual abnormality.For this purpose, the threshold setting unit 507 in this abnormalitydetermining apparatus is constituted to alter the thresholds relating toa paper jam, deterioration of the photosensitive body, and variation inthe image density on the basis of predetermined data input into the datainput unit 504 by the user.

These predetermined data are preferably input by the user in thefollowing manner. A threshold update program is stored in theinformation storage unit 503 in advance. The user is told in advance toactivate this threshold update program by performing a predeterminedoperation on the data input unit 504 using a manual or the like. Whenthe threshold update program is activated by the user operation, displaysuch as “How did you feel about the timing of the abnormalitynotification? Please press the appropriate key. 1: The notification wastoo early, 2: The notification was too late” is displayed on the datadisplay unit 506. When the user presses the corresponding key, displaysuch as “How about the type of abnormality? Please press the appropriatekey. 1: Paper jam, 2: Deterioration of photosensitive body, 3: Variationin image density” is then displayed. When the user presses thecorresponding key, the threshold of the corresponding abnormality isaltered on the basis of the information “the notification was too early”or “the notification was too late”. This information corresponds to theaforementioned predetermined data. In the case of “the notification wastoo early”, the threshold should be increased, and in the case of “thenotification was too late”, the threshold should be decreased.

The threshold setting unit 507 is also constituted to change the generalabnormality threshold in accordance with the rate of change in theMahalanobis distance D serving as the calculation result of the generalabnormality. The reason for this constitution is as follows. FIG. 35 isa graph showing an example of the relationship between the Mahalanobisdistance D of the general abnormality in this copier and the elapsedtime, to which a line of extension has been added to facilitateunderstanding of the manner in which the Mahalanobis distance D changes.In the drawing, a bar graph in the period from a time 12 t to a time 24t comprises a diagonal line which rises to the right in a substantiallyrectilinear fashion, indicating that the rate of change in theMahalanobis distance D per unit time is substantially constant. From thetime 24 t onward, however, the rate of change per unit time begins toincrease with time, and hence the drawing becomes a line graph. A dottedline a in the drawing shows the Mahalanobis distance D if the rate ofchange from the time 24 t to a time 28 t were the same as that from thetime 20 t to the time 24 t. However, it can be seen from the actualgraph that the rate of change increases at a sharp angle. The rate ofchange increases similarly from the time 28 t to a time 32 t, and fromthe time 32 t to a time 36 t. In the illustrated example, similarly tothat of FIG. 31 described above, the general abnormality can no longerbe detected at the time 32 t, when “Mahalanobis distance D<abnormalitydetection threshold” is established, and at the time 36 t, a fault mayoccur before the general abnormality is detected. Therefore, thethreshold setting unit 507 of this abnormality determining apparatusreduces the abnormality detection threshold as shown in the drawing whenthe rate of change increases over two consecutive time periods. As aresult, the abnormality detection threshold used at the time 32 t takesthe new smaller value, enabling the general abnormality to be detectedat the time 32 t. By detecting the general abnormality in this manner,situations in which the occurrence of the general abnormality cannot bepredicted due to a rapid increase in the increase rate of theMahalanobis distance D can be avoided.

Note that instead of changing the general abnormality threshold inaccordance with the rate of change of the Mahalanobis distance D, thefrequency with which the presence of the general abnormality isdetermined may be increased at the point where the Mahalanobis distanceD approaches the general abnormality threshold to a certain extent, asin the abnormality determining apparatus according to the secondembodiment described above. Further, in this abnormality determiningapparatus, the operation display unit 3 of the copier shown in FIG. 4may double as the data input unit 504 and data display unit 506 of theabnormality determining apparatus shown in FIG. 34. Also in thisabnormality determining apparatus, the determination result is output tothe data display unit 506 similarly to the abnormality determiningapparatus according to the second embodiment described above. FIG. 36shows an example of a screen that is output on the data display unit 506when an abnormality relating to deterioration of the photosensitive bodyis detected. This abnormality determining apparatus also comprisessimilar function restricting means to those of the abnormalitydetermining apparatus according to the second embodiment.

In the abnormality determining apparatus according to the secondembodiment, by initially setting at least one of the thresholds relatingto a paper jam, deterioration of the photosensitive body, and variationin the image density, which are used individually in the respectiveprocesses for determining each individual abnormality, in accordancewith information regarding the environment in which the detectionsubject copier is disposed, or in other words by reflectingenvironmental information in the thresholds, it becomes possible, forthe reasons described above, to avoid providing notification of theoccurrence of an abnormality at an inappropriate timing due to a varyingdegree of abnormality perception depending to the environment,regardless of personal differences.

Further, in the abnormality determining apparatus according to thesecond embodiment, by initially setting at least one of the threethresholds in accordance with information regarding the frequency ofmaintenance technician visits to the location in which the copier isdisposed, or information regarding the distance from the maintenanceservice providing organization to the disposal location, it becomespossible to avoid situations in which the timing of abnormalitydetection is delayed inappropriately due to an excessive time lagbetween a request for repairs from the user to the service organizationand the actual departure of the serviceperson to the location of theuser.

Further, in the abnormality determining apparatus according to thesecond embodiment, when replacing an old copier with a new one, byinitially setting the three thresholds used to determine the presence ofan abnormality in the new copier to the same respective values as thethree thresholds of the old copier, it becomes possible, for the reasonsdescribed above, to avoid deterioration of the abnormality detectionprecision caused by initially setting values reflecting the userinformation in a general sense as the thresholds.

Further, in the abnormality determining apparatus according to thesecond embodiment, by updating at least one of the three thresholds inaccordance with information regarding the repair request history of theuser, based on the occurrence of abnormalities, the thresholds can bechanged gradually from their initial setting to values corresponding tothe requirements of the user.

In the abnormality determining apparatuses of the first embodiment andsecond embodiment, the Mahalanobis distance is determined as acalculation result during a calculation process performed in the processfor determining the general abnormality, on the basis of the normalgroup data set stored in the information storage unit 503 serving asinformation storage means and the information obtained by theinformation obtaining unit 501 serving as information obtaining means.By updating the normal data set on the basis of the determination as tothe presence of the general abnormality and the result of an inspectionof the copier, it is possible, for the reasons described above, to avoidmistaken determinations due to the inclusion of non-normal groupedinformation in the normal group data set.

Further, in the abnormality determining apparatus according to thesecond embodiment, by using a device which receives data input of thethresholds transmitted via a communication line as the data input unit504 serving as data input means, data input of the thresholds into theabnormality determining apparatus can be performed by a user in a remotelocation.

In the abnormality determining apparatus according to the modificationdescribed above, by providing the threshold setting unit 507 serving asthreshold setting means, the user need only input user informationrather than the thresholds themselves. As a result, situations in whichthe user is forced to perform complicated calculations in order todetermine the thresholds can be avoided.

In the abnormality determining apparatus according to the modificationdescribed above, the threshold setting unit 507 asks the userpredetermined questions, and obtains user information on the basis ofresponse data input into the data input unit 504 by the user. In sodoing, user information can be drawn from the user in a natural manner,without making the user aware of the need to adjust the abnormalitydetermination precision, and as a result, the thresholds can be setinitially to values which are suited to the user.

In the abnormality determining apparatus according to the modificationdescribed above, the threshold setting unit 507 is constituted to modifythe three thresholds relating to a paper jam, deterioration of thephotosensitive body, and variation in the image density, which are usedrespectively to determine the presence of the individual abnormalities,on the basis of predetermined data input into the data input unit 504 bythe user. With this constitution, for the reasons described above, thethree thresholds can be adjusted little by little on the basis of theactual experience of the user toward values that are perfectly suited tothe user. Further, in the abnormality determining apparatus according tothe modification described above, the threshold setting unit 507 isconstituted to modify the general abnormality determining threshold,which is used to determine the presence of the general abnormality, inaccordance with the rate of change of the Mahalanobis distance D, whichis the calculation result of the general abnormality. By means of such aconstitution, for the reasons described above, situations in whichoccurrence of the general abnormality cannot be predicted due to a rapidrise in the increase rate of the Mahalanobis distance D can be avoided.

In the abnormality determining apparatuses of the second embodiment andthe modification thereof, the abnormality determining unit 502 servingas determining means is constituted to determine the Mahalanobisdistance D on the basis of the normal group data set stored in theinformation storage unit 503, and the obtained results of theinformation obtaining unit 501, and determine the presence of thegeneral abnormality on the basis of the result of a comparison betweenthe Mahalanobis distance D and the general abnormality threshold. Bymeans of this determination, the general abnormality incorporating theplurality of individual abnormalities can be detected easily.

Further, in the abnormality determining apparatus according to thesecond embodiment, the abnormality determining unit 502 is constitutedto modify the frequency with which the presence of the generalabnormality is determined in accordance with the Mahalanobis distance D,which is the calculation result of the general abnormality. By means ofthis constitution, as described above, situations in which occurrence ofthe general abnormality cannot be predicted due to a rapid rise in theincrease rate of the Mahalanobis distance D can be avoided.

Further, in the abnormality determining apparatuses of the secondembodiment and the modification thereof, by providing functionrestricting means for restricting the functions of the copier inaccordance with the type of individual abnormality that has occurred,the copier can be operated to implement printing until preparations forrepairs are complete.

As described above, in the second embodiment and the modificationthereof, the presence of a general abnormality which is capable ofincorporating a plurality of types of abnormality in the detectionsubject is determined. When it is determined that the generalabnormality is present, individual determinations are made as to thepresence of the plurality of abnormalities (to be referred to as“individual abnormalities” hereafter) that may be incorporated into thegeneral abnormality, thus enabling the type of abnormality to bespecified. In so doing, the presence of the individual abnormalitiesneed only be determined when the general abnormality has been confirmedas “present”, rather than determining the presence of all of theindividual abnormalities every time the presence of the generalabnormality is determined, and hence increasingly complicated controlcaused by individual determinations for each type of abnormality can besuppressed. Further, by specifying the type of abnormality that hasoccurred when the general abnormality is determined as“present”,complicated maintenance responses following the determination can beavoided.

Further, the plurality of thresholds required to determine the presenceof the individual abnormalities respectively are subjected to initialsetting in accordance with user information such as proficiency leveland degree of fault perception. In so doing, the presence of eachindividual abnormality can be determined with a precision that is suitedto each individual user.

Further, the plurality of thresholds required to determine the presenceof the individual abnormalities respectively may be initially set orupdated in accordance with user information which is input into the datainput means by a serviceperson or the user. By means of such initialsetting or updating, the presence of each individual abnormality can bedetermined with a precision that is suited to each individual user.

Further, by initially setting or updating the plurality of thresholdsrequired to determine the presence of the individual abnormalitiesrespectively in accordance with user information obtained from the userby threshold setting means, the presence of each individual abnormalitycan be determined with a precision that is suited to each individualuser.

Hence, the presence of an abnormality can be determined with a precisionthat is suited to each individual user while avoiding complicatedcontrol to determine the presence of each type of abnormalityindividually and complicated maintenance responses following thedetermination.

Third Embodiment

The third embodiment mainly serves to achieve the aforementioned thirdobject of the present invention.

Note that FIGS. 1 to 3, 5 to 13, 17, and 18, and the descriptionpertaining to these drawings, which were referenced in the firstembodiment, are also applied substantially to the third embodiment.Accordingly, repetitive description has been omitted, and the particularfeatures of the third embodiment are described in detail.

FIG. 37 shows the basic constitution of an abnormality predicting systemcomprising a state determining apparatus according to the thirdembodiment. A state determining apparatus 801 comprises an informationobtaining unit 802 serving as information obtaining means, an indexvalue calculation unit 803 serving as index value calculating means, anda determination unit 804 serving as change of state determining means.The information obtaining unit 802 obtains a plurality of types ofinformation relating to an image forming operation of an image formingapparatus. The index value calculation unit 803 calculates a singleindex value on the basis of the plurality of types of informationobtained by the information obtaining unit 802. The determination unit804 determines variation in a subsequent state of the image formingapparatus on the basis of data relating to temporal variation in theindex value calculated by the index value calculation unit 803. The datarelating to temporal variation in the index value calculated by theindex value calculation unit 803 and data relating to the determinationresult of the determination unit 804 may be used by a control unit 805which serves as control means for controlling the various devices in animage forming system 806 serving as image forming means, or outputted todisplay means such as a display or an external apparatus.

The information obtaining unit 802 obtains the plurality of informationto be described below, and is constituted by a communication interfaceor the like for performing data communication between various sensorsfor detecting various sensing information, the control unit 805, and animage data processing unit not shown in the drawing. The informationobtaining unit 802 transmits a data obtaining request to the varioussensors, the control unit 805, and the image data processing unit. As aresult, various sensing information data from the various sensors,control parameter information data from the control unit 805, and inputimage information data from the image data processing unit can bereceived.

The control unit 805 is constituted by a CPU, RAM, ROM, an I/O interfaceunit, and so on. The index value calculation unit 803 and determinationunit 804 may be provided separately to the control unit 805 as devicesconstituted by a unique LSI or the like, or may double as hardwareresources constituting the control unit 805, such as the CPU.

The information that is obtained by the information obtaining unit 802and inputted into the index value calculation unit includes sensinginformation, control parameter information, and input image information.The sensing information comprises data obtained by the various sensorsprovided within or around the image forming apparatus. Examples of suchsensing information include the dimensions of each portion of theapparatus, the speed of the moving bodies in the apparatus, time(timing), weight, current value, potential, oscillation, sound, magneticforce, light amount, temperature, and humidity.

The control parameter information is typically information whichaccumulates as the results of control of the apparatus. Examples of thiscontrol parameter information include the user operating history, powerconsumption, toner consumption amount, the setting history of variousimage formation conditions, and the warning history.

The input image information is obtained from information inputted intothe image forming system 806 as image data. Examples of this input imageinformation include the cumulative number of color pixels, the ratio ofthe character portion, the ratio of the halftone portion, the ratio ofcolored characters, the toner consumption distribution in the mainscanning direction, RGB signals (total toner amount per pixel unit), thesize of the original, an original with borders, and the character type(size, font).

The state determining apparatus is constituted by the informationobtaining unit, the index value calculation unit, and the determinationunit. A plurality of types of information such as those indicated in theinput information is obtained in the information obtaining unit, asingle index value is calculated from this information in the indexvalue calculation unit, and a determination as to whether or not theapparatus is normal is performed by the determination unit on the basisof the index value. If the apparatus appears close to an abnormal state,measures such as performing correction control on the image formingsystem through the control unit or issuing and displaying a warning tothe outside are taken. Note, however, that the present invention merelyclaims index value calculation and state determination, and its scopedoes not extend to operations following those of the control unit. Inthe flow of “obtain information→calculate index value→determine state”,information relating to a normal data set gathered in advance isrequired to calculate the index value. This normal data set informationis formed into a matrix and used thus to calculate the index value. Inthe subsequent description, this matrix will be referred to as a“calculation parameter”. The calculation parameter corresponds to thereference space in the MT method (Mahalanobis Taguchi method). Thecalculation parameter is calculated using the following method.

FIG. 38 is a flowchart showing a basic operation of the abnormalitypredicting system constituted as described above. The aforementionedplurality of types of information, which is assumed to be related to thestate of the image forming apparatus, is inputted into the statedetermining apparatus 801 of the abnormality predicting system (step3-1). The plurality of types of information is obtained at a requiredtiming by the information obtaining unit 802, whereupon a single indexvalue is calculated in the index value calculation unit 803 on the basisof the obtained information according to a predetermined calculationmethod (step 3-2). Data regarding temporal variation in the calculatedindex value are used to determine an abnormality, such as a fault, inthe image forming apparatus, or outputted to a display or an externalapparatus (step S3-3).

Before the index value is calculated, the index value calculation method(calculation formula) must be determined. In this embodiment, amultidimensional space is defined with different coordinate axes foreach of the inputted plurality of information, and the index value iscalculated as a distance within this multidimensional space. For thispurpose, a plurality of groups of the plurality of information obtainedin FIG. 37 is determined when the image forming apparatus is operatingnormally.

FIG. 12, which was referenced above, is a flowchart showing a procedurefor determining the calculation method (calculation formula) of theindex value.

First, n groups of k pieces of information thought to be related to thestate of the image forming apparatus are obtained while operating theimage forming apparatus (S1-1). The information is obtained in themanner described above, a specific example of which will be describedhereafter.

FIG. 17, which was referenced above, shows the constitution of the datafor the obtained information. Under the initial condition (for example,the first day, first machine, or similar), k pieces of data areobtained. These are set as y11, y12, . . . , y1 k. The data obtainedsimilarly under the next condition (the second day, second machine, orsimilar) are set as y21, y22, . . . , y2 k, and so on until n groups ofdata are obtained.

Next, the raw data (for example, yij) are normalized for eachinformation type (j) by an average value (yj) and a standard deviation(σj) using the aforementioned Eq. (1) (S1-2). FIG. 18, which wasreferenced above, shows the results of normalization of the data shownin FIG. 17 using Eq. (1).

Next, all of the correlation coefficients rpq (=rqp) between two groupsof data from among the k types of information are determined using theequation shown in Eq. (2), and these correlation coefficients areexpressed as a matrix R, as shown in Eq. (3) (S1-3). An inverse matrixof the correlation coefficient matrix R is then determined, and theresult of this determination is expressed as a matrix A, as illustratedin Eq. (4) (S1-4).

By means of this process, the value of the calculation parameter in thecalculation formula used when calculating the single index value isdetermined. The data sets here all express a normal state, and it istherefore assumed that the various pieces of obtained information have afixed correlation. When the apparatus diverges from a normal state andit appears that an abnormality such as a fault may occur, thesecorrelations become unbalanced such that the “distance” from the origin(stable state average) in the multidimensional space defined asdescribed above increases. This “distance” serves as the index value.

FIG. 13, which was referenced above, is a flowchart showing a procedurefor calculating the index value in the step S3-2 in FIG. 38. The indexvalue at an arbitrary timing is determined in the following manner.First, k types of data x1, x2, . . . , xk in any state are obtained(S2-1). The data types correspond to y11, y12, . . . , y1 k, and so on.Next, the data for the obtained information are normalized using theaforementioned Eq. (6) (S2-2). Here, the normalized data correspond toX1, X2, . . . , Xk. Then, using the calculation formula shown in Eq. (7)(S2-3), which is determined using the element akk of the determinedinverse matrix A, the index value D² is calculated. Note that D, whichis the square root of the index value, is known as a “Mahalanobisdistance”. Further, the symbol Σ in the Eq. (7) denotes the sum relatingto the suffixes p and q.

Note that the processing for determining the calculation method of theindex value, or in other words the calculation formula of the indexvalue, and the processing for calculating and updating the index value Dusing this calculation formula, may be executed continuously while theimage forming system 806 is operative. In the processing flowchart inthis case, the processing steps of FIG. 38 and the processing steps ofFIG. 12 are combined, as shown in FIG. 39.

The description from “(a) Sensing information” to “(c) Input imageinformation” in the first embodiment is applied as is to the types ofinformation to be obtained in order to predict an abnormality in thecopier shown in FIG. 1, to which this embodiment is applied, and themethod of obtaining this information.

Thus the index value D is calculated from these various types ofinformation, and an abnormality such as a fault is predicted bydetermining, on the basis of the index value, the latent possibility ofan abnormality such as a fault occurring. Basically, the possibility ofa fault occurring is determined to be high when the magnitude of theindex value D calculated from the plurality of information as describedabove is greater than a predetermined threshold. This threshold istypically determined in advance through experiment. Alternatively, thethreshold may be set at an arbitrary initial value (10, for example),and then updated as data accumulate.

The index value D is a gauge expressing the degree to which thecorrelation between the obtained information has diverged from a normalstate. As the index value increases, this divergence from the normalstate is determined to be greater. Hence the possibility of a faultoccurring can be forecast even when the faulty mechanism is unclear.

Next, a treatment method, implemented after the index value D has beencalculated and the occurrence of an abnormality has been predicted bydetermining the state of the image forming apparatus on the basis of theindex value D, will be described. Measures such as those cited in thefollowing sections (d) to (j) may be taken following calculation of theindex value and abnormality prediction.

(d) Outputting the Calculation Result, State Determination Result, andAbnormality Prediction Result.

Examples of the content of this output include the calculation result ofthe index value D or a numerical value reflecting the index value, adetermination result indicating a change in the state of the imageforming apparatus, and a prediction result indicating the occurrence ofan abnormality such as a fault or expiration of a component in the formof a warning or the like notifying the user than a fault is about tooccur. Data relating to temporal variation in the value of the indexvalue D or the numerical value reflecting the index value D may beoutputted as a graph. The following methods may be cited as examples ofoutput methods.

-   (d-1) Display of numerical value data or a message on display means    such as a liquid crystal display in an operating unit panel or the    like.-   (d-2) A notification or warning constituted by a voice or a specific    sound pattern that is output by audio output means such as a    speaker.-   (d-3) Recording onto a recording medium (transfer paper).

The results in (d) are outputted to display means or audio output meansprovided in the corresponding image forming apparatus, or recorded ontoa recording medium (transfer paper) and then outputted. The result mayalso be transferred by transmission means to a printer server connectedvia a network, or a monitoring center connected by a communication line,which monitors the state of various apparatuses.

(e) Transferring the Calculation Result, State Determination Result, andAbnormality Prediction Result.

Similar content to that described in (d) may be transferred to a printerserver or monitoring center.

(f) Storing the Calculation Result, State Determination Result, andAbnormality Prediction Result.

Similar content to that described in (d) is stored in a storage device(memory) provided in each image forming apparatus, the printer server,or a device in the monitoring center. The content that is stored in thestorage device may also be read to perform control.

(g) Halting the Device

In cases such as when the calculation result of the index value Dexceeds a predetermined reference value, or the increase rate of theindex value D rises, the image forming apparatus is halted forcibly andmaintenance is requested.

(h) Restricting Operations or Modifying Control.

Related parts of the calculation result of the index value D and thevarious information sources are estimated, and control modification suchas restricting related operations is performed. The following may becited as examples of such control modification.

-   (h-1) Modifying the color mode-   (h-2) Modifying the recording speed-   (h-3) Modifying the halftone screen ruling-   (h-4) Modifying the halftone processing method-   (h-5) Restricting the paper type-   (h-6) Modifying the registration control parameters-   (h-7) Modifying the image Formation process parameters (in the case    of an electrophotographic image forming apparatus, for example, the    charging potential, exposure amount, development bias, transfer    bias, etc.).    (i) Replenishing or Replacing Consumables or Components

Replenishment or replacement is performed automatically on the basis ofthe calculation result of the index value D.

(j) Automatic Repair

When the presence of an abnormality is determined in a specific sitefrom both the index value D and the various information sources, a modeis executed to perform repairs on the specified site.

In this embodiment, individual index values or a single common indexvalue are determined prior to product shipment using the copier shown inFIGS. 1 to 3, and following shipment, the index value is monitoredonline so that maintenance can be performed when the index valueincreases. As for the specific content of the types of information to beobtained and the method of obtaining this information, the descriptionin the first embodiment from “(1) Temperature” to “(5) Photosensitivebody uniform charging potential (for four colors)” and (7) Colored arearatio (for four colors) is applied thereto as is.

In this embodiment, the following description is also added.

(7) LD Drive Current

The drive current value of an LD (laser diode) which performs imageexposure is monitored according to color on a drive circuit, and used.

(8) Total Counter (Cumulative Number of Print Screens Per Color)

Cumulative data obtained by counting the number of print screens foreach color are used. For example, when one screen is formed in fullcolor mode, Y, M, C, and Bk increase by one count each, and when onescreen is formed in monochrome (black) mode, only Bk increases by onecount. In Y and M modes, only Y and M increase by one count. These dataare stored in a storage element, and the results are used.

(9) Development γ Value

A graded latent image potential is formed on the photosensitive bodiesin a test mode, and by developing the latent image under specificconditions, a graded density pattern is formed. This is read by areflection density sensor, and a relationship between the potential(potential difference) and the developed reflection density isdetermined. The gradient thereof is set as the γ value. This value isdetermined for each color, and used.

(10) Development Starting Voltage

The relationship between the potential and the developed reflectiondensity is determined in the test mode described above, and a potentialat which development reaches zero is determined by extrapolation. Theresult is set as the development starting voltage. This value isdetermined for each color, and used.

In this embodiment, the following test was implemented. A test printerwas prepared, and a running test emulating various usage modes wasperformed in a laboratory. During the test, the 10 items and 30 types ofdata described above were gathered several times every day. A part ofthe gathered data is shown in FIG. 40.

In actuality, 50 groups of data were gathered, and during that time,operations continued with no particular problems.

Calculations using the aforementioned Eq. (1) to Eq. (6) were performedon the basis of the data to determine the calculation parameter in Eq.(7). Using the result of this determination, the average value of D ofthe 50 groups obtained during a normal operation was approximately 1.Thus the calculation method (calculation formula) of the index value Dwas defined.

Next, following the sale of products manufactured on the basis of thetest machine, continuous monitoring of these products was performed onthe market. The obtained data were identical to those of the previoustest.

FIG. 41 is a graph showing movement (temporal variation) in the indexvalue D calculated in this embodiment. In FIG. 41, the timing at which aproblem (abnormal state) occurs in the image forming apparatus isindicated by the arrow. In this case, the problem that occurs is tonerfilming onto the photosensitive body. The index value D rises prior tothe occurrence of this abnormality. From this result, it can be seenthat there is a close correlation between an increase in the index valueD and the occurrence of an abnormality, and hence by following thetemporal variation data of the index value D, this problem (tonerfilming) can be predicted prior to its occurrence. In other words, anapproaching change in the state of the printer can be determined on thebasis of temporal variation in the rising index value D, and thus theremaining amount of time before the index value D reaches a value atwhich the problem (toner filming) occurs can be learned. Hence it ispossible not only to determine the presence of the problem (tonerfilming), but also predict the remaining amount of time before theproblem (toner filming) occurs.

Note that in this embodiment, the image forming apparatus is connectedto a monitoring system via a communication line, and the value of theindex value D is transmitted to the monitoring system constantly. In themonitoring system, setting is performed to monitor variation in theindex value D and issue a warning when the index value D begins toincrease and exceeds a specific value. When a warning is issued, apotential fault is considered to be present, and hence a servicepersonis dispatched to perform maintenance. The serviceperson checks the stateof the image forming apparatus directly, and takes necessary measuressuch as component replacement, or electrical and mechanical adjustments.After taking these measures, the serviceperson confirms that the valueof the index value D is within the normal range, whereupon maintenanceis complete. Further, the value of the index value D or a commentcorresponding thereto is displayed at all times, and thus the user isinformed of the state and encouraged to perform preliminary maintenance.

As described above, by using this calculation parameter, defined by thenormal data set alone, the index value can be calculated from the inputinformation data sets obtained thereafter, the obtained index valuehaving a characteristic whereby it increases in value when the inputinformation data set used in the calculation differs from the normaldata set of the calculation parameter. In other words, the index valueincreases as the apparatus diverges from a normal state, and thischaracteristic can be used to determine the state of the apparatus. Theindex value corresponds to a Mahalanobis distance in the MT method,having a value of approximately one in a normal state, and graduallyincreasing in an abnormal state. A value of approximately 3 is typicallyused as a threshold between a normal and an abnormal state.

A flowchart for deriving the calculation parameter is shown in FIG. 42,and a flowchart for calculating the index value and determining thestate of the apparatus is shown in FIG. 43.

In the calculation parameter derivation method shown in FIG. 42, firstvarious input information is obtained (step S501) This input informationis the sensing information (a), control parameter information (b), inputimage information (c) and so on, shown in FIG. 37. Next, the state ofthe image forming apparatus while these data are obtained is determinedseparately by some means (step S502). As the determination means, amanual determination performed by the operator or an automaticdetermination performed by a sensor may be employed. If, as a result ofthe determination, the machine is determined to be normal (step S502-Y),the input data information is accumulated as normal data (step S503),and if the machine is determined to be abnormal, the machine is repaired(step S504), whereupon information gathering is restarted. If the stateof the machine is normal, normal data are accumulated gradually, andwhen a fixed amount of data has been gathered or a data gathering periodhas elapsed (step S505-Y), calculation parameter derivation is performed(step S506) to determine the calculation parameter. Note that there is alower limit to the fixed amount of data whereby, if there are k types ofinput information data, then k+1 groups of data must be gathered. Thisis a required condition for determining the calculation parameter as aninverse matrix.

In the index value calculation and state determination method shown inFIG. 43, first the various input information are obtained similarly toFIG. 42 (step S601). The input information types must be exactly thesame as the input information types from which the calculation parameteris derived. If the number of types is different, the index value cannotbe calculated normally, and if different types of input information aregathered, even if the number of types is the same, the calculationparameter becomes meaningless, and hence it becomes impossible toperform a state determination using the calculated index value. In thecase of index value calculation, the index value is calculated everytime information is inputted (step S602).

The timing of information input is set, for example, at a fixed numberof printed sheets, a certain time every day, or in another manner.During index value calculation, the calculation parameter derived inFIG. 42 is used to determine whether or not the state of the apparatusis normal on the basis of the magnitude of the determined index value(step S603). The index value threshold used during a determination istypically set to approximately 3, as noted above, but the threshold maybe set independently according to the system to which it is applied, thetypes of input information, and a user-requested level. If the indexvalue is equal to or less than the threshold, the entire machine isdetermined to be normal (step S604), and if the index value exceeds thethreshold, the machine is determined to be approaching an abnormal state(step S605). If the index value greatly exceeds the threshold (reachinga two-figure or three-figure value), the machine is determined to be ina definite abnormal state. Thus in the aforementioned statedetermination method, state determinations are performed according tothe flows shown in FIGS. 42 and 43. Note that in the case of abnormalityprediction, temporal variation in the index value is monitored in orderto predict the time at which a definite abnormality is due to occur, andhence this is basically identical to the state determination methodillustrated in FIGS. 42 and 43.

In this type of image forming apparatus, the plurality of types ofinformation to be obtained are, as described above:

(a) Sensing Information

Developer information (toner concentration, fluidity, bulk density,electric resistance, consumption amount, remaining amount, and so on),photosensitive body information (surface potential, color,irregularities, coefficient of friction, electric resistance value, andsoon), paper conveyance information (deviation in the conveyance timing,vibration noise during conveyance, and so on), paper information(strength, thickness, surface condition, moisture content, and so on),driving information (rotation speed, drive current, drive noise, andsoon), output image information (density, γ characteristic, halftonereproducibility, and so on), environment information (temperature,humidity, airflow, atmospheric composition, and so on), etc;

(b) Control Parameter Information

Image formation parameters (various bias values, light amount, linearspeed, fixing temperature, and so on), user scanning history, powerconsumption, consumption amount of combustibles, etc; and

(c) Input Image Information

Pixel number, character ratio, halftone portion ratio, color ratio, fontinformation, etc.

By gathering this information continuously during a normal operationwhen the image forming apparatus has been shipped onto the market and isin use, the precision of the calculation parameter can be raised. Thecalculation parameter is an index expressing the normal state of theapparatus, and hence ideally should include all possible combinations ofdata that are determined as being in a normal state. If a certain normaldata combination is not included in the calculation parameter, the indexvalue calculated in relation to that normal data combination will take alarge value, and hence the data combination will be determined asabnormal. To avoid this, the normal data set from which the calculationparameter is derived must include all possible combinations of normaldata. However, it is impossible to prepare such a normal data set priorto shipment of the apparatus since the environment in which theapparatus will be placed at the user destination and the manner in whichthe apparatus will be used cannot be predicted. In consideration of thispoint, the normal data set is gathered continuously at the userdestination following shipment of the apparatus, and the calculationparameter is derived and fixed only when a sufficient amount of data hasbeen gathered.

To realize this continuous gathering of the normal data set, means mustbe provided for determining whether or not the image forming apparatusis in a normal state. In this embodiment, image quality detecting meansfor detecting the image quality of an output image are provided in orderto determine whether or not the image forming apparatus is operatingnormally. The image quality detecting means may take either a line formsuch as a CCD, or a spot form such as a P sensor. A line sensor such asa CCD is required for measuring the image quality of the entire outputimage, but since a large data amount is produced, image qualitycalculation processing increases in bulk, and hence under the currentcircumstances, a spot sensor is more realistic. It should be noted,however, that a line sensor such as a CCD is also suitable for anapplication such as that of the present invention, in which speed is notrequired. The image quality detecting means are disposed so as to detectthe medium onto which the toner image is formed, more specifically onthe photosensitive body, the intermediate transfer body, the transferpaper, or a similar position. The most appropriate disposal position forchecking the operational state of the entire apparatus is on the finaloutput medium, or in other words the transfer paper, and hence bydetecting the image quality on the transfer paper, the state of theentire apparatus can be learned. Note, however, that a method ofproviding image quality sensors on the intermediate transfer body andphotosensitive body, and checking conditions downstream thereof withindividual sensors, may also be considered.

(11) Image quality detection

Here, an outline of an image quality detecting sensor will be provided.

1. Outline of Image Quality Detection

First, an outline of image quality detection will be provided withreference to FIGS. 44 to 54.

1.1 General Outline

The basic constitution of the entire image forming apparatus serving asthe subject of image quality detection is as described in FIG. 1, andthe main parts of the image forming unit are as illustrated in FIG. 2.

Note that in FIG. 1, a full color apparatus using a four-drum tandemtype intermediate transfer method is shown as an example of the imageforming apparatus, but this is merely a representative example of animage forming apparatus, and as will be described below, a full colorapparatus using a four-drum tandem type direct transfer system, asingle-drum type intermediate transfer system, or another system may beused. The present invention may also be applied to a direct transfertype monochrome apparatus or an image forming apparatus using anothersystem.

1.2 Image Quality

FIGS. 44 and 45 are enlarged photographs (for convenience ofdescription, binarization processing was implemented during imagecapture) showing a halftone dot image (the size of one halftone dot is[2 pixels×2 pixels]) formed on transfer paper by the image formingapparatus shown in FIGS. 1 and 2, comprising a 600 dpi writing system.FIG. 44 shows an initial image PT1, and FIG. 45 shows an image PT2following printing performed over an extremely long period of time undercertain conditions. The initially uniform halftone image PT1 shown inFIG. 44 becomes the rough halftone image PT2 shown in FIG. 45 due tovarious factors such as deterioration of the developer andphotosensitive body during the long image-creating process. Theroughness of the halftone image PT2 in FIG. 45 may be quantified as aspatial frequency characteristic of the fine density unevenness andexpressed as a characteristic value such as “granularity”, for example.

An image having a high degree of granularity (high graininess) is animage showing great roughness, and an image having a low degree ofgranularity (low graininess) is a uniform image showing littleroughness. However, not all density unevenness can be perceived visuallyas roughness, and as long as no sense of roughness is perceived by thehuman eye, the image quality of a printed image may be deemedsatisfactory. The spatial frequency characteristic of the sight of anaverage trial subject in relation to density unevenness is shown in FIG.46*. It is known that the spatial frequency at which density unevennesscan be perceived by the human eye is limited to a spatial frequencyrange of 0 [cycle/mm] to approximately 10 [cycle/mm], with a peak ofapproximately 1 [cycle/mm], as noted above.

FIG. 47 is a view showing an outline of the constitution of an imagequality detecting apparatus for measuring fine density unevenness in animage. In the drawing, an image quality detecting apparatus 900comprises a reflection type optical sensor (photo-reflector) 910, anamplifying circuit 920 for amplifying an electric signal from thereflection type optical sensor 910, a calculation circuit 930 serving ascalculating means for performing predetermined calculation processing onthe basis of the signal that is amplified by the amplifying circuit 920,and a signal generating circuit 940 serving as signal generating meansfor generating a signal required for optical recording control on thebasis of the calculation output of the calculation circuit 930. Thereflection type optical sensor 910 comprises an LED (light-emittingdiode—light-emitting element) 901 serving as a light source, a condenserlens 902 for condensing the light emitted from the LED 901 to a lightbeam having a predetermined beam diameter, a photoelectric converterelement (light-receiving element) 903 for receiving reflection lightfrom an image pattern 951 on an image carrier 950 and converting thereflection light into an electric signal, and an imaging lens 904 forforming the reflection light from the image pattern 951 into an image onan image forming surface of the photoelectric converter element 903. Ascan be seen from the characteristic diagram in FIG. 48, showing therelationship between distance in the scanning direction (the beamdiameter) and light amount, the reflection type optical sensor 910 usesa reflection type optical sensor in which the irradiation beam diameteris narrowed to a spot light SP.

The reflection type optical sensor 910 condenses an irradiation beamfrom the light source constituted by the LED 901 using the condenserlens 902 such that the circular beam diameter on the surface of theimage pattern 951 formed on the image carrier 950 reaches approximately400 [μm]. The light that is reflected therefrom is detected by thephotoelectric converter element 903, such as a photodiode, and thusadhesion unevenness of toner particles 952 within the image pattern 951can be grasped as variation in the light amount entering thephotoelectric converter element 903.

Variation in the light amount corresponding to the toner adhesion amountmay be learned by a method of detecting this variation according todifferences in the specular reflection characteristic or irregularreflection characteristic of the toner particles and the surface of theimage carrier, a method of detecting this variation according todifferences in the reflection spectroscopy characteristic of the tonerparticles and the image carrier surface, and so on. By combining thesemethods, highly sensitive detection can be performed. When differencesin the specular reflection characteristic or irregular reflectioncharacteristic are used, a material having a high degree of glossinessand a strong specular reflection characteristic is preferably used forthe surface of the image carrier 950 due to the typically strongirregular reflection characteristic of a toner image. When detection isperformed according to differences in the reflection spectroscopycharacteristic, a light source wavelength at which the reflectionspectroscopy characteristic of the toner particles 952 differs greatlyfrom the reflection spectroscopy characteristic of the surface of theimage carrier 950 is preferably used. The measuring apparatus in FIG. 47uses the LED 901 having a light-emitting wavelength of 870 [μm], and inthis case, a detection method using the difference in their regularreflection characteristic of the toner particles 952 and the surface ofthe image carrier 950 is implemented. The beam diameter (d1 in FIG. 48)relating to the scanning direction of at least the spot light SP must beset to no more than 1 [μm] so that density unevenness of approximately 1[cycle/mm], which is the most sensitive value in the spatial frequencycharacteristic of the human eye shown in FIG. 46, can be detected. Thisbeam diameter d1 is derived from the inverse 1 [μm] of the maximum value1 [cycle/mm] of the spatial frequency in FIG. 47, and here, the beamdiameter d1 is set at approximately 400 [μm]. The beam diameter d1 isdefined here as the distance between points on the two sides of thelight beam at which the power per unit area of the spot light SP on thebeam irradiation surface falls to a maximum value of 1/e.

FIGS. 44 and 45 described above show an example of the constitution ofan image creating process of the image forming apparatus in which thereflection type optical sensor (image quality sensor) 910 shown in FIG.47 is disposed opposite an intermediate transfer belt immediately afterthe developing process. Scanning of the image on the photosensitive bodyby the spot light SP is performed by driving the photosensitive body torotate, and the reflection light output when the images PT1, PT2 shownin FIGS. 44 and 45 are scanned in the paper conveyance direction (thelongitudinal direction in the drawings) is detected. The state ofvariation in the light amount (voltage) of the reflection light from theamplifying circuit 920 is shown in FIG. 49. The scanning conditions ofthe spot light SP at this time area scanning speed of 200 [μm/s], ascanning distance of approximately 11 [mm], and a data sampling cycle of75 [μs]. In other words, the sampling pitch on the image isapproximately 15 [μs], and scanning is performed only once, withoutincluding an averaging process or the like. Note that by determining theaverage light amount value in FIG. 52, the average adhesion amount ofthe toner particles 952 adhering to the pattern can be calculated.

1.4 Visual Noise (Image Quality)

1.4.1 Noise Amount Calculation

With the state of output shown in FIG. 49, where an amount of light isoutput with time as a parameter, the spatial frequency characteristic ofimage density unevenness cannot be read, and therefore the spatialfrequency characteristic is calculated by the calculation circuit 930.Well-known means such as fast Fourier transformation (FFT) arepreferably applied to calculate the spatial frequency characteristicfrom the point of view of processing speed. The transformation result ofthe fast Fourier transformation is shown in FIG. 50. Note that the peakseen at 6 [cycle/mm] in FIG. 50 is due to the repetition frequency ofthe dot pattern in FIGS. 44 and 45.

As can be seen from FIG. 46, the visual characteristic is extremelysensitive to density unevenness having a spatial frequency in thevicinity of 1 [cycle/mm], and therefore, by comparing this to the noiseamount in the vicinity of 1 [cycle/mm] in FIG. 50, for example, thedegree of deterioration in the image quality of the pattern (image PT2)shown in FIG. 45 from the pattern (image PT1) shown in FIG. 44 can belearned. When a deterioration in image quality is detected in thismanner, signal generation is performed by the signal generating circuit940 in the measuring apparatus shown in FIG. 47 in order to effectappropriate control of the image forming conditions. This signal isreceived, whereupon the image forming conditions are controlledautomatically by a control circuit CON of the image forming apparatusMFP shown in FIG. 47, and thus automatic control is performed to restorenormal image quality to the greatest extent possible.

When image quality restoration is deemed impossible by automatic controlalone, the control circuit CON instructs on a display device, not shownin the drawing, that parts such as the developer and photosensitive bodybe exchanged, and thus encourages parts exchange. In so doing, the lifespan of the developer, photosensitive body, and so on can be extended toa maximum. Moreover, since the size of minimum required pattern isapproximately 1 [μm]×approximately 10 [μm], the amount of toner consumedby pattern image formation can be held to a minimum.

1.4.2 Visual Noise Amount Calculation

After obtaining the spatial frequency characteristic in FIG. 50,weighting of the visual spatial frequency characteristic shown in FIG.46 is performed on the spatial frequency characteristic by thecalculation circuit 930 to determine the visual noise amount. FIG. 51shows the relationship between the visual noise amount and the spatialfrequency, and illustrates the state of output of the visual noiseamount by the calculation circuit 930. Weighting is performed bymultiplying the characteristic shown in FIG. 51 to the characteristicshown in FIG. 50. As a result of this calculation, the visual spatialfrequency characteristic alone can be extracted, and hence the targetimage quality detection can be performed easily. Moreover, the signalportion appearing in the vicinity of 6 [cycle/mm] caused by the imagepattern structure can be eliminated, and hence information which isunrelated to the image quality under observation can be removed. Byremoving such information which is unrelated to the image quality, theoccurrence of detection errors can be substantially eliminated.

1.4.3 Total Visual Noise Amount

By integrating the visual noise amount shown in FIG. 51 for a spatialfrequency range of 0.2 [cycle/mm] to 4 [cycle/mm] using the calculationcircuit 930, a total visual noise amount is calculated, as shown in FIG.52. With this value, the total image quality variation oversubstantially the entire spatial frequency range that is perceivedvisually can be learned.

Note that an image quality evaluation pattern to be described belowpreferably uses an approximately 50% halftone image. This is due to thefact that graininess is striking. First, continuous density variationdata in the sub scanning direction of the image pattern are gathered inthe case of a monocular sensor such as that shown in FIG. 47, or in thecase of a line sensor, continuous density variation data in the mainscanning direction are gathered. When a monochrome sensor is used,continuous data on only a specific wavelength (color) are gathered, andwhen a color sensor is used, continuous data on a plurality ofwavelengths (colors) are gathered.

The gathered continuous data are Fourier transformed as described aboveto obtain a density variation power spectrum. The visual spatialfrequency characteristic (VTF) is multiplied by the square root of thepower spectrum (the amplitude of the variation), and then weighting ofthe density variation based on the visual characteristic is performed inthe frequency range described above. By integrating the weighted densityvariation amount, the granularity is determined. Thus granularity isdetermined using density as a reference. Recently, however, thegranularity of brightness, which has a favorable linearity with thehuman eye, has been employed. Hence, to determine the granularity ofbrightness, first the density data must be converted into brightnessdata. Further, to determine color granularity, the granularity iscalculated using color information in addition to brightnessinformation. Thus graininess information is determined from densityvariation data. By performing feedback control on the basis of thegraininess information determined in this manner, images having a stablegraininess can be outputted continuously.

To detect the image quality on the basis of density unevenness, insteadof the pattern shown in FIG. 44, a pattern may be used in which dotshaving a minimum unit of 600 dpi form a single unit of 2 pixels×2pixels, and a repetition cycle z1 of the dot array in the scanningdirection of the spot light SP is set at approximately 170 [μm] (aspatial frequency f1 is approximately 5.9 [cycle/mm], for example). Whensuch a pattern is scanned by the spot light SP having a beam diameter ofapproximately 400 [μm], as described above, a spectrum appears at aspatial frequency in the vicinity of 6 [cycle/mm], as in FIG. 50. Toprevent the spectrum generated by the image pattern itself fromoverlapping with the detection range of the image quality detectionsignal, the repetition cycle z1 of the dot array in the scanningdirection must be set at less than 250 [μm], and preferably less than200 [μm]. Hence in this case, z1=170 [μm].

In either case, to detect the image quality as shown by the flowchart inFIG. 54, to be described below, an image quality detection function maybe realized by a computer program comprising a step of forming an imagepattern on the aforementioned image carrier, a step of irradiating theimage pattern with a spot light, a step of scanning the image patternwith the spot light to detect the amount of light that is reflected bythe image pattern, and a step of detecting the image quality on thebasis of the detected light amount. This computer program is used afterhaving been recorded onto a computer-readable recording medium, ordownloaded from a server or the like via a network.

Note that this control is executed by a CPU of the control circuit ofthe image forming apparatus MFP on the basis of an output signal fromthe signal generating circuit 940 of the image quality detectingapparatus 900. The CPU executes the various processes on the basis of aROM, not shown in the drawing, or a downloaded program, using a RAM, notshown in the drawing, as a work area. The program data are downloaded toa storage device such as a hard disk, not shown in the drawing, orupgraded from a server via a network, not shown in the drawing, or froma recording medium such as a CD-ROM or SD card, for example, via arecording medium driving device, not shown in the drawing.

FIG. 53 shows the disposal positions of the image quality sensor (imagequality detecting means). A disposal position 1 is on the photosensitivebody, a disposal position 2 is on the intermediate transfer belt, adisposal position 3 is on an unfixed image on the transfer paper, and adisposal position 4 is on a fixed image on the transfer paper. Asdescribed above, the disposal position 4 is ideal, but in this case, thepatch pattern for detecting the image quality must be formed on thetransfer paper, and hence may be unacceptable to the user. When theimage quality sensor is disposed on the photosensitive body or theintermediate transfer belt, the formed toner image can be cleaned by thecleaning devices disposed on the respective photosensitive bodies, andhence these disposal positions are unproblematic in terms of the load(transfer paper) on the user. In this case, however, the final outputimage cannot be checked, and hence when the image quality is detected atthe sensor disposal position 2, for example, the state of the imageforming apparatus must be determined comprehensively after addingindividual information such as the secondary transfer current value, thefixing temperature, and the transfer paper conditions.

FIG. 54 is a flowchart showing the flow of data processing in the imagequality sensor.

The output of a light receiving unit (step S701) which receives lightfrom the CCD sensor 903, spot light sensor, or the like is amplified toa desired value by the amplifier (amplifying circuit) 920 (step S702),and this value is converted into digital data by an A/D converter (stepS703). Fourier transformation (FFT calculation) is then performed by thecalculation circuit 930 (step S704) to obtain frequency band data. TheVTF, which is the human sight characteristic, is then superposed ontothe frequency band data (step S705), whereupon the data for thefrequency band that is perceivable to the human eye are weighted.Finally, only the data for the frequency band that is sensitive to thehuman eye are integrated (step S707), and thus a numerical value of theimage quality is obtained.

Thus image quality information is obtained. However, it is a fact thatdifferent levels of image quality are demanded by users. In normaloffice use, the required degree of image quality is not so high, but ina design-related office, a corresponding degree of image quality isrequired. In other words, a corresponding image quality threshold mustbe set for a user who demands high image quality, and the machine mustbe determined as abnormal when the threshold is exceeded. Hence,allowable image quality information of the user must be pre-stored as athreshold in storage means within the apparatus to serve as a referencefor determining whether or not the image quality detected and calculatedby the image quality detecting means is normal. This allowable imagequality information may be determined by showing the user image qualitysamples upon delivery of the apparatus, for example, and may then bestored in the storage means of the image forming apparatus through inputby a serviceperson, by reading the image quality samples with a scanner,or by a similar method.

When a plurality of types of information are obtained continuously inorder to calculate the calculation parameter using the threshold of theallowable image quality information determined for each user as areference, the threshold of the allowable image quality information maybe determined by a method such as that described above. A flowchart usedwhen information is obtained continuously using the threshold as areference is as shown in FIG. 42. At the first condition bifurcation “Isthe state of the machine normal?” (step S502), the image qualitydetected by the image quality detecting apparatus 900 is compared to thethreshold of the allowable image quality information for each user,stored in advance in the storage means. If the image quality is equal toor less than the threshold, the apparatus is determined to be normal,and if not, the apparatus is determined to be abnormal. Information isobtained continuously only when the apparatus has been determined to benormal. When the apparatus is determined to be abnormal, repairs areperformed separately, whereupon information obtaining is resumed (stepsS501 to S503). As normal data accumulate, the data accumulation amountor accumulation period reaches a prescribed amount, whereupon thecalculation parameter is derived therefrom and fixed (steps S503 toS506). Once the calculation parameter has been fixed, there is no longerany need to gather normal data for the calculation parameter, and hencethe state of the image forming apparatus MFP no longer need bedetermined by the image quality detecting apparatus 900. Hence in thepresent invention, the image quality detecting apparatus 900 isconstituted separately to the main body of the image forming apparatusMFP as an additional unit which may be detached from the main body ofthe image forming apparatus following determination of the calculationparameter after the image forming apparatus MFP has operated on themarket for a fixed time period.

The image quality detecting means serving as an additional unit may beloaned to the user from a maker, for example, and removed by the makerwhen it is no longer needed. The merits of this on the user side arethat by installing the additional unit for a fixed time period, afunction is obtained for predicting the occurrence of an abnormality bydetermining the state of the machine, by removing the unit once thisfunction has been established, space is not occupied by the unit, theunit need not be purchased, and so on. The merits on the maker side arethat the image quality detecting means can be recycled, the imagequality detecting means do not have to be sold to the user, and so on.It may be said that these merits are closer to business model meritsthan technological merits.

FIG. 55 is a view showing an example of the specific constitution of theimage quality detecting apparatus when constituted as a separateadditional unit 700.

In this example, the additional unit 700 has both a paper discharge trayfunction and an image quality detecting function. A conventional paperdischarge tray 720 onto which paper is discharged along a normaldischarge path 710 is disposed on top of the additional unit 700, and abox-shaped container 730 is disposed therebelow. The additional unit 700is constituted similarly to a normal paper discharge tray that isattached to the main body of the image forming apparatus, and is alsoconnected to the image forming apparatus main body side electrically.Accordingly, communication means are interposed between the twocomponents in order to notify the image forming apparatus main body sideof image quality detection information. During a normal printingoperation, transfer paper is discharged onto the upper paper dischargetray 720. However, during an operation to gather normal data for thecalculation parameter, an image quality detection mode is activated todetermine the state of the image forming apparatus, and hence dischargepath switching means 750 of the additional unit 700 open automaticallyto switch to a discharge path leading into the interior of theadditional unit 700, or in other words an image quality detectiondischarge path 740.

Conveyance rollers 760 and an image quality sensor 770 are disposed atan inlet portion inside the additional unit 700, and the transfer papercarrying a patch pattern for image quality detection, which is conveyedfrom the image forming apparatus, is stabilized by the conveyancerollers 760 and thus drawn into the additional unit 700. The patchpattern is then read by the image quality sensor 770 disposed at thesubsequent stage, whereupon a numerical value of the image quality iscalculated by a calculation unit not shown in the drawing. Having passedthe image quality detection sensor 770 unit, the transfer paper isstacked onto an image quality detection sample storage unit 780. Thevolume of the image quality detection sample storage unit 780 isdetermined in accordance with the time required to gather the pluralityof types of information for calculating the calculation parameter, andhence the user does not have to remove the sample following detection.Once sufficient data have been gathered, the additional unit 700 isremoved together with the image quality detection samples stacked in itsinterior, whereupon the normal paper discharge tray 720 is disposed inits place.

Note that the image quality calculating unit may be disposed in thevicinity of the image quality sensor, or the calculation unit of theimage forming apparatus main body may be used. Moreover, although notillustrated in detail in the drawing, the additional unit comprising theimage quality sensor may be attached in an easily removable manner inthe image quality sensor disposal positions shown in FIG. 53, andremoved by a serviceperson after use. In this case, the additional unitfunctions only as an image quality sensor, but may be usedsatisfactorily as long as it is disposed so as to be easily removable.

Determining the fixed time period for gathering the calculationparameter data corresponds to the determination of “Have sufficient dataaccumulated?” in the step S505 of the flowchart in FIG. 42. When thetime period is determined according to the number of output sheets, thedetermination condition of “Have sufficient data accumulated?” becomes adetermination condition of “Have X sheets been printed?”.

This method is considered the most straightforward. For example, dataare gathered at fixed sheet number intervals while counting the numberof sheets by monitoring the output of a discharge sensor or a writestarting signal, and when a certain number of sheets has been reached,data gathering ends. In this case, the calculation parameter includesinformation relating to deterioration of the durability of the imageforming apparatus when the apparatus is driven for a periodcorresponding to a fixed number of sheets. A case in which the timeperiod is determined according to a integrated value of thephotosensitive body rotation speed is similar conceptually to sheetnumber management.

In this case, the data gathering interval corresponds to an interval ofa fixed rotation speed integrated value, and data gathering ends when acertain rotation speed integrated value is reached. In this case also,the calculation parameter comprises information relating todeterioration of the durability of the apparatus. These methods can besaid to be data gathering methods using the operating time of theapparatus as a reference, and when employed, information relating todeterioration of the durability of the apparatus can be included asdesired. However, variation in the disposal environment of the machineis believed to affect the gathered data, and when a data gatheringmethod based on the operating time is employed, the influence ofenvironmental variation may offset the data. In this case, if theapparatus is disposed in a different environment (or the environmentchanges greatly due to a change of season), the apparatus may bedetermined to be abnormal when operating normally. To avoid this, thetime period may be determined by a number of operating days.

In this case, the reference is a number of days, and hence a method ofgathering data at certain times and a certain number of times per day,for example, may be employed. When the reference is the number ofoperating days, the calculation parameter may include the effect ofenvironmental variation during the set number of days. Particularly whenthe time period determined according to the number of operating days isset at one year, environmental information for all four seasons, spring,summer, fall, and winter, is incorporated into the calculationparameter, and hence the calculation parameter has a high degree ofreliability in relation to environmental variation. However, thedemerits of this are that a period of one year is too long (both as theperiod up to the beginning of fault prediction after fixing of thecalculation parameter, and as the loan period of the image qualitydetecting means), and that variation occurs in the operating time of themachine, leading to irregularities in the effect of the durabilitydeterioration information of the apparatus.

With a user who prints a small number of sheets, deterioration of theapparatus may not progress such that normal data can only be obtained ina small range. Conversely, with a user who prints a large number ofsheets, deterioration of the apparatus may progress so far that a faultoccurs, causing an obstruction to normal data gathering. Alternatively,the time period may be set up to the point at which the amount of datareaches an arbitrary value. In this case, the data gathering intervalmust be determined using a desired method (with the operating time orthe number of days as a reference), but since the calculation parameteris derived from a fixed amount of normal data, the amount of parentpopulation data is always sufficient. Moreover, the image qualitydetecting means may be removed as soon as the minimum required dataamount has been secured, and hence the image quality detecting means canbe operated efficiently. This method, in which the time period is basedon the amount of gathered data, is believed to be most rational.

As described above, there are various ways of determining the timeperiod, but in actuality, these methods may be combined. Basically, theamount of data for calculating the calculation parameter has a lowerlimit, and hence the most realistic method is presumably to gather datawhile counting the amount of data, and when the lower data amount limitis secured, define the time period based on the operating time or thenumber of days. In certain cases, the operating time reference and thenumber of days reference may also be combined.

When the plurality of types of obtained information and the detected andcalculated image quality information are transmitted to an externalinformation processing apparatus over a communication line, the externalinformation processing apparatus refers to a printer sever or amonitoring center of a maker, for example. The aim of transmitting thegathered data to the external information processing apparatus is todetermine a calculation parameter for a collective of image formingapparatuses using the data for a plurality of image forming apparatusesgathered in the external information processing apparatus. Sinceinformation from a plurality of image forming apparatuses is gathered inthe external information processing apparatus, it is possible todetermine, for example, a calculation parameter for an office floorunit, a calculation parameter for each industrial sector using themachine, a calculation parameter for each geographical area, acalculation parameter for each machine type, and so on.

By determining a calculation parameter for a collective of image formingapparatuses in this manner, a calculation parameter which is suited toeach collective can be determined, thereby improving the reliability ofstate determination. Moreover, the state of the plurality of imageforming apparatuses can be learned with a certain fixed level as areference, and this can be used to set an order of priority forserviceperson visits, for example.

According to this embodiment as described above, the following effectsare achieved.

-   (1) Once the image forming apparatus has been shipped onto the    market and is in a state of usage in the user environment, the    parent population of the normal data set used to derive the    calculation parameter is increased, and thus normal data sets    achieving various balances under the influence of the user    environment are included in the parent population. As a result, the    reliability of state determination can be increased.-   (2) Means for determining whether or not the image forming apparatus    is in a normal state must be provided in order to gather data sets    during a normal operation. By disposing image quality detecting    means as these determining means, the determination as to whether or    not the apparatus is normal can be made using an output image as a    reference. As a result, data gathering can be performed continuously    during a normal operation.-   (3) The image quality detecting means quantify the image quality at    the point of detection, but whether or not a user will be satisfied    with the resulting image quality depends on the user. Hence, by    researching the acceptable image quality level of the user during    apparatus delivery, and storing this information as a threshold in    storage means inside the apparatus, the state of the apparatus can    be determined as normal or abnormal according to the image quality    level demanded by the user. Further, by performing fault prediction    corresponding to each user in a similar manner, measures can be    taken before the user feels dissatisfied, and hence the number of    printed sheets that are discarded due to poor image quality can be    suppressed, which is meritorious in terms of saving resources.-   (4) By gathering a plurality of types of data only when the image    forming apparatus is determined to be in a normal state using the    acceptable image quality of the user as a threshold, a calculation    parameter corresponding to the image quality level required by the    user is determined, and thus the state of the apparatus can be    determined in accordance with each individual user.-   (5) The image quality detecting means are used to derive the    calculation parameter, and are therefore unnecessary once the    calculation parameter has been determined. By constituting the image    quality detecting means separately to the main body of the image    forming apparatus as an external additional apparatus, the image    quality detecting means can be removed by a service person after    use. By loaning the image quality detecting means to the user, the    user can obtain a function for predicting a fault in the machine    automatically after a fixed time period, and need not keep the    unnecessary apparatus attached to the machine on a permanent basis.    The maker is able to reuse the image quality detecting means on an    image forming apparatus newly introduced onto the market, and only    has to manufacture the image quality detecting means as necessary.    By reusing the image quality detecting means, the load on the    environment is not increased.-   (6) By defining the time period for the calculation parameter to    stabilize according to an output number of sheets or an integrated    value of the photosensitive body rotation speed, reflecting the    actual operating state of the apparatus, the state of deterioration    in the durability of the apparatus (an indication of the degree to    which the apparatus deteriorates in relation to the usage amount)    can be reflected in the calculation parameter.-   (7) By defining the time period for the calculation parameter to    stabilize according to a reference number of days, environmental    variation, which causes disturbance, can be reflected in the    calculation parameter. Particularly by setting the number of days at    one year, temperature and humidity variation throughout the year can    be reflected in the calculation parameter, and hence seasonal    determination errors can be eliminated.-   (8) The data from which the calculation parameter is derived are    gathered while the image quality is determined to be normal by the    image quality detecting means, and hence when the time period is    defined by the number of output sheets or a reference number of    days, the size of the parent data population cannot be prescribed.    By setting the time period as a fixed period up to the point at    which the parent data population for deriving the calculation    parameter reaches a fixed size, the image quality detecting means    can be reused efficiently.-   (9) By transmitting the plurality of types of information regarding    the image forming apparatus and the image quality information to an    external information processing apparatus, the state of a plurality    of image forming apparatuses can be monitored by the external    information processing apparatus.-   (10) By deriving a calculation parameter for a collective of image    forming apparatuses in the external information processing apparatus    using the information of a plurality of image forming apparatuses,    calculation parameters can be derived for individual machine types,    individual industry sectors of users, individual geographical areas,    and so on, for example.

As described above, according to the third embodiment, determinations asto whether or not an operation of the image forming apparatus is normalare made by detecting the image quality of the final output paper usingan image quality sensor, and hence the calculation parameter can befixed at an arbitrary timing once a plurality of types of informationhas been obtained continuously over time on the market. As a result,elements showing signs of abnormality can be determined.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

1. An abnormality determining method comprising: an information storingstep for storing information about an object in information storagemeans; an information obtaining step for obtaining information about anobject using information obtaining means; and a determining step fordetermining the presence of an abnormality in a detection subject on thebasis of the stored information in said information storage means andthe obtained information obtained by said information obtaining means,wherein, in said information storing step, a normal group data set,which is a collection of normal value combinations of groupedinformation constituted by a plurality of different types ofinformation, is stored in said information storage means, in saidinformation obtaining step, at least two or more sets of groupedinformation, comprising first grouped information constituted by aplurality of different types of information and second groupedinformation having a different combination to that of said first groupedinformation, are obtained by said information obtaining means, and insaid determining step, a Mahalanobis distance is determined for each setof grouped information on the basis of said normal group data set andthe obtained results of each set of grouped information, and used todetermine the presence of an abnormality in the detection subject.
 2. Anabnormality determining method comprising: an information obtaining stepfor obtaining information about an object using information obtainingmeans; a determining step for determining the presence of an abnormalityin a detection subject on the basis of the obtained information obtainedby said information obtaining means; a calculating step for performing apredetermined calculation on the basis of the obtained informationobtained by said information obtaining means in said determining step;and a comparing step for comparing the calculation result of saidcalculating step to a predetermined threshold, an abnormality beingdetermined to be present when, in said comparing step, said calculationresult has reached said threshold, exceeds said threshold, or fallsbelow said threshold, wherein a general abnormality determining step fordetermining the presence of a general abnormality, which is capable ofincorporating a plurality of types of abnormality, by comparing one ofsaid calculation results obtained on the basis of a plurality of typesof said obtained information to said threshold, and an individualabnormality determining step for determining, only when said generalabnormality is determined as present in said general abnormalitydetermining step, the presence of one of a plurality of types ofabnormality that is incorporated into said general abnormality bycomparing one of said calculation results obtained on the basis of atleast one of said plurality of types of obtained information to saidthreshold, are implemented in said determining step, and initial settingis performed on at least one of a plurality of said thresholds, usedindividually in each of said individual abnormality determining steps,in accordance with information regarding a user of said detectionsubject.
 3. The abnormality determining method as claimed in claim 2,wherein initial setting is performed on at least one of said pluralityof thresholds used individually in each of said individual abnormalitydetermining steps in accordance with information about the environmentin which said detection subject is disposed.
 4. The abnormalitydetermining method as claimed in claim 2, wherein initial setting isperformed on at least one of said plurality of thresholds usedindividually in each of said individual abnormality determining steps inaccordance with information regarding the frequency of maintenancetechnician visits to a location in which said detection subject isdisposed, or information regarding a distance from a maintenance serviceproviding organization to said disposal location.
 5. The abnormalitydetermining method as claimed in claim 2, wherein, when said detectionsubject is replaced, said plurality of thresholds used individually ineach of said individual abnormality determining steps for determiningthe presence of an abnormality in the new detection subject are setinitially to respectively identical values to said plurality ofthresholds used individually in each of said individual abnormalitydetermining steps for determining the presence of an abnormality in theold detection subject.
 6. The abnormality determining method as claimedin claim 2, wherein at least one of said plurality of thresholds usedindividually in each of said individual abnormality determining steps isupdated in accordance with information regarding a repair requesthistory of the user based on abnormality occurrence.
 7. The abnormalitydetermining method as claimed in claim 2, wherein a Mahalanobis distanceis calculated as said calculation result in said calculating step ofsaid general abnormality determining step, on the basis of a normal dataset stored in said information storage means and the obtainedinformation obtained by said information obtaining means, and saidnormal data set is updated on the basis of whether said generalabnormality is determined to be present in said general abnormalitydetermining step, and a result of an inspection of said detectionsubject.